An Introductory Course of Quantitative Chemical Analysis / With Explanatory Notes

SILVER BY THE T

thiocyanate as a white, curdy precipitate. If ferric nitrate is also present, the slightest excess of the thiocyanate over t

ions invo

KNO_{3}, 3KSCN + Fe(NO_{3})

s but very little dissociated in aqueous solutions, and the characteristic c

i.e., a gram-molecular weight of the salt or 97.17 grams. If the ammonium thiocyanate is used, the amount is 76.08 grams. To prepare the solution for this determination, which should be approxim

nd add 5 cc. of dilute nitric acid (sp. gr. 1.20). Abou

ARDIZ

ortions of about 0.5 gram each and dissolve them in 50 cc. of water. Add 10 cc. of dilute nitric acid which has been recently boiled to expel the lower oxides of nitrogen, if any, and then add 5 cc. of the indicator solution.

late the relation of the thio

t, therefore, be standardized against silver nitrate (or pure silver), e

h is expelled on drying. If the nitrate has come into contact with o

if many titrations of this nature are to be made. In the absence of such a solution the liability of passing the end-p

ION OF SIL

. gr. 1.2) and boil until all the nitrous compounds are expelled (Note 1). Cool the solution, dilute to 50 cc., and add

cyanate solution required, calculate

d silver in known quantity to the solution. The liquid must be cold at the time of titration and entirely free from nitrous compounds, as these sometimes cause a reddening of the indicator soluti

well as those from the standardization, should be placed in

RT

ETRIC

L DIRE

render this separation as complete as possible; and finally, the segregation of that substance, commonly by filtration, and the determination of its weight, or that of some stable product formed from it on ignition. For example, the gravimetric determination of aluminium is accomplished

rs. In order to avoid burdensome repetitions in the descriptions of the various gravimetric procedures which follow, certain general instructions are introduced at thi

portant instrument in gravimetric analysis,

IPIT

easily established, and which separate from solution in such a state that they can be filtered readily and washed free from adm

d washing, it is often desirable to allow a precipitate to remain for some time in contact with the solution from which it has separated. The solution is often kept warm during this period of "digestion." The small crystals gradually disappear and the larger cry

cult to filter and wash. Substances of this class also exhibit a tendency to form, with pure water, what are known as colloidal solutions. T

when circumstances permit. The slow addition is less likely to occasion contamination of the preci

S AND

bestos filter in a perforated porcelain or platinum crucible, commonly known, from its originator, as a "Gooch filter." The operation and use of a

h. The filters employed should be washed filters, i.e., those which have been treated with hydrochloric and hydrofluoric acids, and which on in

pendix. It should always be placed so that the upper edge of the paper is about one fourth inch below the top of the funnel. Under

column of liquid which, by its hydrostatic pressure, produces a gentle suction, thus materially promoting the rapidity of filtration. Unle

elain cone or a small "hardened filter" of parchment, and the tendency of the precipitates to pass through the pores of the filter, more than compensate for the possible gain in time. On the other hand, filtration by suction may be useful in the

ND WASHING O

age of a liquid through the pores of a filter is retarded by friction, and

should touch the side of the receiving vessel to avoid loss by spa

d precipitate which shows no tendency to pass through the filter at first, while the solution is relatively dense, appears at once in the washings. Under such conditions the advantages

is then decanted through the filter, so far as practicable without disturbing the precipitate, and a new portion of wash-water is added. This procedure can be employed to special advantage with gelatinous precipitates, which fill

ally that the washing is most !rapidly! accomplished by filling the filter well to the top with wash-water each time, and allowing it to drain completely after e

oval of foreign matter is effected. They are likely to shrink and crack,

can be secured. Every original filtrate must be tested to prove complete precipitation of the compound to be separated, and the wash-waters must also be tested to assure complete removal of foreign material. In testing the latter, the amount first taken shoul

m !each precipitate! of a series simultaneously treated must be tested, since the rate of washing will o

during filtration is one to be commended. On this paper a record of the numb

precipitates until the completion of an analysis, in order that, in

rub the sides of these vessels to loosen the adhering particles. This can best be done by s

ICC

triangle, or an iron triangle covered with silica tubes, to support the crucible or other utensil

essential in special cases; but for most purposes the calcium chloride, if renewed occasionally and not

ny length of time. The dehydrating agents rapid

CIB

washing, in order to remove moisture, or to convert it through physical or chemical changes into some definite and stable form for weighing. Crucibles to be used in fusion processes must be made of materials which will withstand the action of the fluxes employed, and crucibles to be used for ignitions must be made of mate

ossibility of the reduction to the metallic state of metals like lead, copper, silver, or gold, which would alloy with and ruin the crucible. When platinum cruci

his reagent. Acid sulphate fusions, which require comparatively low temperatures, can sometimes be made in platin

n account of their smaller coefficient of expansion. Ignition of substances not

ver crucibles are u

ble that it is liable to theft unless constantly under the protection of the user. As constant protection is often difficult in instructional laboratories, it is advisable, in order to avoid

N OF CRUCI

ht. The amount and weight of this moisture varies with the humidity of the atmosphere, and the latter may change from hour to hour. The air in the desiccator (see above) is kept at a constant and low humidity by the drying agent wh

thin the desiccator is strongly heated and expands before the desiccator is covered. As the temperature falls, the air contracts, causing a reduction of air pressure within the covere

Gentle polishing of the surface destroys the crystalline structure and prevents further damage. If sea sand is used for this purp

oride. If the former is used, care should be taken not to heat so strongly as to expel all of the sulphuric acid, since the normal sulphates somet

OF PREC

dried without loss of time to the analyst (as, for example, over night), it is well to submit them to this process. It should, n

the precipitate, its moisture content, and temperature to which it is to be hea

OF CHLORINE IN

h the Use of a

eneath the first in the notebook. The difference of the two weights represents the weight of the chloride taken for analysis. Again weigh a second portion of 0.25-0.30 gram into a second beaker of the same size as the first. The beakers should be plainly marked to correspond with the entries in the notebook. Dissolve each portion of the chloride in 150 cc. of distilled water and add about ten drops of dilute nitric acid (sp. gr. 1.20) (Note 2). Calculate the volume of silver nitrate solution required to effect complete precipitation in each case, and add slowly about 5 cc. in excess of that amount, with constant stirring. Heat the solutions cautiously to boiling

el a perforated porcelain crucible (Gooch crucible), making sure that when the crucible is gently forced into the mouth of the funnel an airtight joint results. (A small 1 or 1-1/4-inc

RATION:

in thickness, is formed. A gentle suction must be applied while preparing this felt. Wash the felt thoroughly by passing through it distilled water until all fine or loose particles are removed, increasing the suction at the last until no more water can be drawn out of it; place on top of the felt the small, perforated porcelain disc and hold it in place by pouring a very thin l

disturbing the asbestos felt. When pouring liquid onto a Gooch filter hold the stirring-rod at first well down in the crucible,

aker as far as possible. Wash the precipitate twice by decantation with warm water; then transfer i

suction at the flask and remove the funnel or filter tube from the suction flask. Hold the end of the tube over the mouth of a small test tube and add from a wash-bottle 2-3 cc. of water. Allow the water to drip through into the test tube and add a drop of dilute hydrochloric acid. No precipitate or cloud should form in the wash-wate

been cut in pieces of about 0.5 cm. in length. After digestion, the asbestos is filtered off on a filter plate and washed with hot, distilled wat

chloride to carry down with it other substances which might be precipitated from a neutral

action between the nitric acid and the sodium chloride is possible, by which a loss of chlorine, either as such or as hydrochloric acid, might ensue. The presence o

in diffused daylight is not sufficient to materially affect the accuracy of the determination. It should be noted, however, that a slight error does result from the effect of light upon the silver chloride precipitate and in cases in wh

of the finest quality and capable of division into minu

alt is completely removed when the wash-water shows no evidence of silver. It must be borne in mind that silver chloride is somewhat soluble in hydrochl

imits, and is about 0.0018 gram per liter at 18°C. for the curdy variety usually precipitated. The chloride is als

er nitrate was added in excess, may be set aside. The silver can b

d on the same filter, without the removal of the preceding portions, until the crucible is about two thirds filled. If the felt is properly prepared, filtration and washing are rapidly accompli

h the Use of a

e Appendix). Pour the liquid above the precipitates through the filters, wash twice by decantation and transfer the precipitates to the filters, finally washing them until free from silver solution as described. The funnel should then be covered with a moist

over the precipitate on the glazed paper with a watch-glass to prevent loss of fine particles and to protect it from dust from the air. Fold the filter paper carefully, roll it into a small cone, and wind loosely around !the top! a piece of small platinum wire (Note 2). Hold the filter by the wire over a small porcelain crucible (which has been cleaned, ignited, cooled in a desiccator, and weighed), ignite it, and allow the ash to fall into the crucible. Place the crucible upon a clean clay triangle, on its side, and ignite, with a low flam

slowly raised until the silver chloride just begins to fuse at the edges (Note 3). The crucible is then cooled in a desiccator and weighed, after which the heating (without the addition of acids) is repeated, and it is again weigh

of acids, would be accompanied by some difficulty. The small amount of silver reduced from the chloride adhering to the filter paper after separating the bulk of the precipitate, and igniting the paper as prescribed, can be dissolved in nitric acid, and completely re

eration to avoid contact with any reduced silver from the reduction of the precipit

tilization is possible at high temperatures. The temperature of fusion is not always sufficie

AND OF SULPHUR IN FERR

H_{4}){2}SO

NATION

lution cautiously into about 200 cc. of water, containing a slight excess of ammonia. Calculate for this purpose the amount of aqueous ammonia required to neutralize the hydrochloric and nitric acids added (see Appendix for data), and also to precipitate the iron as ferric hydroxide from the weight of the ferrous ammonium sulphate taken for analysis, assuming it to be pure (Note 4). The volume thus calculated will be in excess of that actually required for precipitation, since the acids are in part consumed in the oxidation process, or are volatilized. Heat the solution to boiling, and all

of the washings, acidified with nitric acid (Note 5), show no evidences of the presence of chlorides when tested with silver nitrate. The filt

of crystallization; and also those which are red, indicating the presence of ferric iron. If, on the other hand, the value of an average sa

ult is, in effect, the formation of some ferric hydroxide which tends to separate. Moreover, at the boiling temperature, the ferric sulphate produced by the oxidation hydrolyzes in part with the formation of a basic ferric sulphate, which also tends to

ormed in the "ring-test" for nitrates. The nitric oxide is driven out by heat, and the solution then shows by its color the presence of ferric compounds. A drop of the oxidized solution shoul

ed in this oxidation are perhaps m

-}+ 4H^{+} -> 3Fe^{

his case either the nitric or the hydrochloric acid. The

Cl -> 2Fe_{2}(SO_{4}){3}

h nitric acid is added t

A gradual neutralization with ammonia would result in the local formation of a neutral solution within the liquid, and subsequent deposition of a basic sulphate as a consequence of a local deficiency of OH^{-} ions from the NH_{4}OH and a partial hydrolysis of the ferric salt. Even with this precaution the entire absence of sulphates fr

f ammoniacal liquids upon glass, the iron precipi

ed with nitric acid, before testing with silver nitrate, to

is permissible, though not prescribed. The precipit

f the Iron

ool it in a desiccator and weigh, repeat

transfer it cautiously to the crucible. Wipe the inside of the funnel with a small

o the crucible and dries the precipitate without danger of loss as the result of a sudden generation of steam within the mass of ferric hydroxide. As the drying progresses the burner may be gradually moved toward the base of the crucible and the flame increased until the paper of the filter begins to char and

rucible still inclined on its side, but without the cover (Note 1). Finally set the crucible upright in the triangle, cover it, and heat at the full temperature of a

_{2}O_{3}) calculate the percentage

mportance to insure the reoxidation to ferric oxide of any iron which may be reduced to magnetic oxide (Fe_{3}O_{4}) during the combustion o

r removal from the desiccator. In all weighings after the first it is well to place the weights upon the balance-pan

ribed, with the additional precaution that the solution must be boiled until it contains but a very sligh

dissolve in an excess of the caustic alkalies and form anions, probably of the formula AlO_2^{-} and CrO_{2}^{-}. Chromium hydroxide is reprecipitated from this solution on boiling. When first precipitated the hydroxides are all readily soluble in acids, but aluminium hydroxide dissolves with considerable difficulty after standing or boiling for so

ATION OF

ously add hydrochloric acid until the solution shows a distinctly acid reaction (Note 1). Heat the solution to boiling, and add !very slowly! and with constant stirring, 20 cc. in excess of the calculated amount of a hot barium chloride solution, containing about 20 grams BaCl_{2}.2H_{2}O per liter (Notes 2 and 3). Continue the boiling for about two minutes, allow the precipitate to settle, and decant the liquid at the end of half an hour (Note 4). Replace the beaker containing

ssociation of sulphuric acid in the presence of the H^{+} ions of the hydrochloric acid, and possibly because of the formation of a compl

olved in the precipitation of

O_{4}^{-} -

l be seen that nearly all of the barium sulphate has been precipitated, and that the small amount which then remains in the solution which is in contact with the precipitate must represent a saturated solution for the existing temperature, and that this solution is comparable with a solution of sugar to which

c'n SO_{4}^{-})/(Conc'

ion) the concentration of the Ba^{++} ions is much increased, and as a consequence the !Conc'n SO_{4}! must decrease in proportion if the value of the expression is to remain constant, which is a requisite condition if the law of mass action upon which our argument depends holds true. In other words, SO_{4}^{-} ions must combine with some of the added Ba^{++} ions to form [BaSO_{4}]; but it will be recalled that the solution is already saturated with BaSO_{4

pitant. This is also notably true in the case of nitrates and chlorates of the alkalies, and of ferric compounds; and, since in this analysis ammonium nitrate has resulted from the neutralization of the excess of the nitric acid added to oxidize the iron, it is essential

tion of a complex ion (Fe(SO_{4})_{2}) which precipitates with the Ba^{++} ion, while Richards (!Zeit. anorg. Chem.!, 23, 383) ascribes it to hydrolytic action, which causes the formation of a basic ferric complex whi

erefore, the sulphur alone were to be determined in the ferrous ammonium sulphate, the precipitation by barium mig

e at the end of a half-hour, and the solution may safely be filtered

llow the precipitate to stand in a warm place for several hours, if practicable, to promote ease of filtration. The filtrate and washings should always be carefully examined for minute quantities of the sulphate w

e taken to prevent any considerable reduction from this cause. Subsequent ignition, with ready access of air, reconverts the sulphide to sulphate unless a considerab

or its solution. It is not decomposed at a red heat but suffers

OF SULPHUR IN

t of filter paper, the latter being placed in the crucible. Cover the crucible and heat until a quiet, liquid fusion ensues. Remove the burner, and tip the crucible until the fused mass flows nearly to its mouth. Hold it in that position until the mass has solidified. When cold, the material may usually be detached in a lump by tapping the crucible or gently press

to gentle boiling for about three minutes (Note 2). Filter off the carbonate and wash it with hot water, testing the slightly acidified washings for sulphate and preserving any precipitates which appear in these tests. Acidify the filtrate w

hate, calculate the percentage

nces ordinarily insoluble in acids into two components, one of which

CO_{3}, -> BaCO_{

arbonate insoluble, a separation between them is possible an

ated by most of the substances mentioned in Note 3 on page 114. The impurities pass into the water solution together w

ll of the sodium sulphate solution has been removed by filtration that the reversion of some of the barium carbonate to barium sulphate is prevented. This is an application of the principle of mass action, in w

PHOSPHORIC ANHY

cium chloride, or fluoride. Specimens are easily obtainable which are nea

nsoluble in ammoniacal solutions, this procedure cannot be applied directly. The separation of the phosphoric acid from the calcium must first be accomplished by precipitation in the form of ammonium phosphomolybdate in nitric acid solution, using ammonium molybdate as t

licic acid alone interferes with the precipitati

OF AMMONIUM PH

with warm water, using as little as possible (Note 2). Receive the filtrate in a beaker (200-500 cc.). Test the washings with ammonia for calcium phosphate, but add all such tests in which a precipitate appears to the original nitrate (Note 3). The filtrate and washings must be kept as small as possible and should not exceed 100 cc. in volume. Add aqueous ammonia (sp. gr. 0.96) until the precipitate of calcium phosphate first produced just fails to redissolve, and then add a few drops of nitric acid until this is again brought into solution (Note 4). Warm the solution until

cc. of ammonia solution (sp. gr. 0.96) with 325 cc. of ni

t for a few hours. It should then be carefully examined for

nalyses. It is obvious that the larger the amount of substance taken for analysis the less will be the relative loss or gain due to unavoidable experimental errors; but, in this instance, a check is placed upon the amount of material which may be taken both by the bulk of the res

e with the phosphomolybdate, although not in combination with moly

eutralizes the acid which holds the calcium phosphate in solution and causes precipitation; but after the removal of the p

ent action, while ammonium nitrate lessens the solubil

e tends to separate molybdic acid from the solution. This acid is nearly white, and its deposition in the filtrate on long standing should not be mistaken for a second precipitation of the yello

ut it is better, when practicable, to allow the solution to stand for this length

en precipitated under the conditions prescribed in the procedure. Whatever other variations may occur in its composition, the ratio of 12 MoO_{3}:1 P seems to hold, and this fact is utilized in volumetric processes for the determination of

F MAGNESIUM AMM

to boiling. Calculate the volume of magnesium ammonium chloride solution ("magnesia mixture") required to precipitate the phosphoric acid, assuming 40 per cent P_{2}O_{5} in the apatite. Measure out about 5 cc. in excess of this amount, and pour it into the acid solution. Then add slowly dilute ammonium hydroxide (1 volume of strong ammonia (sp. gr. 0.90) and 9 volumes of water), stirring constantly until a precipitate forms. Then add a volume

ure of one volume of concentrated ammonia and three volumes of water. It is not necessary to clean the beaker co

ntaining one fourth of its volume of concentrated aqueous ammonia (sp. gr. 0.90) and this proportion should be carefully maintained as prescribed in the procedure

e phosphate to carry down molybdic acid. The tendency of the magnesium precipitate to carry down molybdic acid is also increased if the solution is t

sential, and the stirring not less so. Stirring promotes the separation of the precipitate and the formation of larger crystals, and may therefore be substitute

IGNITION OF MAGNESIU

ution of the precipitate in acid and precipitation of the molybdenum by sulphureted hydrogen, after which the magnesium precipitate may be again thrown dow

nesia mixture, and then dilute ammonium hydroxide solution (sp. gr. 0.96), drop by drop, with constant stirring, until the liquid smells distinctly of ammonia. Stir for a few moments and then add a volume of strong ammonia (sp. gr. 0.90), equal to one third of the volume of the solution. Allow the solution to stand for some hours, and then filter off the magnesium ammonium p

equences both to the crucible, if of platinum, and the analysis. Do not raise the temperature above moderate redness until the precipitate is white. (Keep this precaution well in mind.) Ignite finally at the highest temperature of the Tirrill burner, and repeat the heating until the weight is constant. If the ignited precipitate is persistently discolored b

2}P_{2}O_{7}) obtained, calculate the phosphoric

volved in the precipitation

4}^{+} + Mg^{++} -

phosphoric acid may dissociate, the HPO_{4}^{-} or H_{2}PO_{4}^{-} ions, exhibit the characteristics of very weak acids, in that they show almost no tendency to dissociate further i

4}^{+} + PO_{4}^{--} -

{4}^

ty in the formation of the new ion, HPO_{4}^{-}, and this continu

onium phosphate loses ammonia and water an

Mg_{2}P_{2}O_{7}

danger here lies in a possible reduction of the phosphate by the carbon of the filter paper, or by the ammonia evolved, which

S OF LI

imestones in small quantities, and an exact qualitative analysis will often show the presence of sulphides or sulphates, phosphates, and titanates, and the alkali or even the heavy metals. No attempt is made in the following procedures to provide a complete quantitative scheme which would take into accou

ATION OF

is. Since it is essential that the seller and buyer should make their analyses upon comparable material, it is customary for each analyst to determine the moisture in the sample examined, and then to calculate the percentages of th

f an hour, after cooling in a desiccator, until the loss of weight after an hour's heating does not exceed 10 milligrams. It should be noted that a variatio

THE INSOLUBLE M

te 2). Evaporate to dryness on the water bath. Pour over the residue a mixture of 5 cc. of water and 5 cc. of concentrated hydrochloric acid (sp. gr. 1.2) and again evaporate to dryness, and finally heat for at least an hour at a temperature of 110°C. Pour over this residue 50 cc. of dilute hydrochloric acid (one volume acid (sp. gr. 1.12) to five volumes water

ed percentage of the

ccuracy in the determination of the ingredients which are present in small proporti

epend upon the strength of acid used for solution of the limestone. It cannot, therefore, be rega

ange is not complete after one evaporation. The heating at a temperature somewhat higher than that of the water bath for a short time tends to leave the silica in the form of a powder, which promotes subsequent filtration. The s

inum crucible with about six times its weight of anhydrous sodium carbonate, and the procedure given on page 151

C OXIDE AND ALUMINIUM

on and keep the solution warm until it barely smells of ammonia; then filter promptly (Note 2). Wash the filter twice with hot water, then (after replacing the receiving beaker) pour through it 25 cc. of hot, dilute hydrochloric acid (one volume dilute HCl [sp. gr. 1.12] to five volumes water). A brown residue insoluble in the acid may be allowed to remain on the filter. Wash the filter five times with hot water, add to the filt

age of the combined o

hydroxide and to precipitate manganese as MnO(OH)_{2}. The solution must contain not more than a bare excess of hydro

en the bromine is added, as strong ammonia reacts

om the air, with consequent partial precipitation of the calcium as carbonate. This is possible even under the most favorable conditions, and for this rea

ter weighing, with about ten times its weight of acid potassium sulphate, solution of the cold fused mass in water, and volumetric determination of the iron,

cipitate may be dissolved in acid before ignition, and the separation effected by special m

ATION OF

graduation by means of a strip of filter paper, make the solution uniform by pouring it out into a dry beaker and back into the flask several times. Measure off one fifth of this solution as follows (Note 1): Pour into a 100 cc. graduated flask about 10 cc. of the solution, shake the liquid thoroughly over the inner surface of the small flask, and pour it out. Repeat the same operation. Fill the 100 cc. flask until the lowest point of the meniscus is exactly level with the mark on its neck, remove any

cium oxalate to settle for a half-hour, and decant through a filter. Test the filtrate for complete precipitation by adding a few cubic centimeters of the precipitant, allowing it to stand for fifteen minutes. If no preci

ng to boiling, and add 1 cc. ammonium oxalate solution (Note 5) and ammonia in slight excess; boil for two minutes, and set aside for a half-hour. Filter off the calcium oxalate upon the filter first used, and wash free from chlor

arters of an hour in a platinum crucible at the highest heat of the Bunsen or Tirrill burner, and finally for ten minutes at the blast lamp (Note 6). Repeat the hea

he calcium precipitate may be converted into calcium sulphate by placing 2 cc. of dilute sulphuric acid in the crucible (cold), heating t

age of the calcium (Ca) in the limestone, remembering that only

d be greater than could be properly treated. The solution is, therefore, diluted to a definite volume (5

e slightly acid immediately after filtration, in order to av

after filtration, and reprecipitation in the presence of only the small amount of magnesium which was included in the first precipitate. When, however, the proportion of magnesium is not very large, the second precipitation of the calcium ca

te are exceedingly simple, and the principles discussed in connection with t

+ Ca^{++} ->

with the latter there is almost no tendency to diminish the concentration of C_{2}O_{4}^{-} ions by the formation of an acid less dissociated than the acetic acid itself, and practically no solvent action ensues. When a strong mineral acid is present, however, the ionization of the oxalic acid is much r

and the oxalic acid) to form water, leave the Ca^{++} and C_{2}O_{4}^{-} ions in the solution to recombine to form [CaC_{2}O_{4}], which is precipitated in the absence

sists mainly of CaC_{2}O_{4

econd precipitation of the calcium oxalate to insure the presence of a slight

alate loses carbon dioxide and carb

2}O -> CaO + CO_

in a platinum crucible at the highest temperature of a Tirrill burner, but it is well t

as described, will convert most of the calcium oxalate to calcium carbonate,

4} -> CaCO

O_{4} -> CaSO_{4}

s conversion to sulphate is to be preferred, as a com

e sulphuric acid, warming, and titrating the liberated oxalic acid with a standard solution of potassium permanganate as described on page 72.

ATION OF

evaporated to very small volume. The solution should be carefully examined at this point and must be filtered if a precipitate has appeared. Heat the clear solution to boiling; remove the burner and add 25 cc. of a solution of disodium phosphate. Then add slowly dilute am

e 2), except that 3 cc. of disodium phosphate solution are added before the reprecipitation of the magnesium ammonium phosphate instead of the magnesia mixture there prescribed. From the weigh

o the total volume of solution should be carefully provided for, on account of the relative solubility of the magnesi

salts. The difficulty can best be remedied by filtering the precipitate and (without washing it) redissolving in a small quantity of hydrochloric acid, from which it may be again thrown down by ammonia after adding a li

er involving a long procedure, and a redetermination of the magnesium fr

ION OF CAR

tion Ap

ration:

the bottom of the evolution flask (B) and having its lower end bent upward and drawn out to small bore, so that the carbon dioxide evolved from the limestone cannot bubble back into (b). The evolution flask should preferably be a wide-mouthed Soxhlet extraction flask of about 150 cc. capacity because of the ease with which tubes and stoppers may be fit

sulphuric acid (sp. gr. 1.84). The short rubber tubing (d) connects the first U-tube to a second U-tube (E) which is filled with small dust-free lumps of dry calcium chloride, with a small, loose plug of cotton

the side toward the evolution flask and one half of the other side are filled with small, dust-free lumps of soda lime of good quality (Note 3). Since soda lime contains considerable moisture, the other half of the right sid

wo thirds full (Note 4). A small tube containing calcium chloride is connected with the Geissler bulb proper by a ground joint and should be wired to the bulb for safety. This is designe

e absorption of water vapor by (F) or (F') and serves as an aid in regulating the flow of air through the apparatus. (H) is an aspirator bottle of about

r sulphate solution. The addition of concentrated sulphuric acid to this solution reduces its vapor pressure so far that very little water is carried on by the air current, and this slight amount is absorbed by the calcium chloride in (E). As the calciu

mber of determinations to be made successively is small. The potash bulbs will usually permit of a larger number of su

bonates, with the evolution of water. Considerable heat is generated by the reaction, and the temperature of t

nalytical purposes should be used. The tube should n

apor pressure of the solution, thus lessening the danger of loss of water with the air which passes through the bulbs. The small quantity of moisture which is then carried

ratus, potassium bicarbonate is formed, and as it is much less soluble than the carbonate, it often p

Ana

o stand for 30 minutes in the balance case, and wiping it carefully with a lintless cloth, taking care to handle it as little as possible after wiping (Note 1). Connect the

ass through (D) or (G) after a few seconds. When assured that the fittings are tight, close (h) and open (a) cautiously to admit air to restore atmospheric pressure. This precaution is essential, as a sudden inrush of air will project liqu

be (K) and open (a). Then close (k) and open (h), regulating the flow of water from (H) in such a way that about two bubbles per second pass through (G). Place a small flame under (B) and !slowly! raise the contents to boiling and boil for three minutes. Then remove the burner from under (B) and continue to draw air through the apparatus for 20-30 minutes, or until (H) is e

ing (H), the apparatus is rea

nt of moisture absorbed on the surface is as nearly constant as practicable during two weighings, and a uniform temperature is also assured. The stopcocks of the U-tube should

tion apparatus, some carbon dioxide may be carried thr

ions resulting are Ca^{++} and CO_{3}^{-}. In the presence of H^{+} ions of the mineral acid, the CO_{3}^{-} ions form [H_{2}CO_{3}]. This is not only a weak acid which, by its formation, diminishes t

h is distributed through the apparatus, is swept out into the absorption bulb by the current of air. This air is pur

EAD, COPPER, IRON,

YTIC SEP

al Dis

of any particular ion depends upon the potential (voltage) of the current which is passing through the solution, since for each ion there is, under definite conditions, a minimum potential below which the discharge of the ion cannot be effected. By taking advantage of differences in discharge-potentials, it is possible to effect separations of

which is measured in amperes, and corresponds to the volume of water passing a cross-section of a stream in a given time interval; and third, the resistance of the conducting medium, which is measured in ohms. The relation between these three fa

ctrode actually occurs. The current strength determines the rate of deposition and the physical characteristics

lues given below are those required for deposition from normal solutions at ordinary temperatures with reference to a hydrogen electrode. They must be regarded a

{4} +0.77 +0.42 +0.34 +0.33 +0.1

t be applied, that is, +1.56 volts. The deposition of zinc from a solution of zinc sulphate would require +2.67 volts, but, since the deposition of hydrogen from sulphuric acid solution requires only +1.90 volts, the

he electrodes, somewhat higher voltages are required to attract and discharge them. From this it follows that the concentrations should be kept as high as possible to effect complete deposition in the least practicable time, or else the potentials applied must be progressively increased as deposition proceeds. In practice, the desired resul

rent applied, will also begin to separate. For example, from a nitric acid solution of copper nitrate, the copper ions will first be discharged at the cathode, but as they diminish in concentration hydrogen ions from the acid (or water) will be also discharged. Since the hydrogen thus liberated is a reducing agent, the nitric acid in the solution is slowly reduced to ammonia

s, since liberated chlorine attacks the electrodes. In some cases, as for example, that of silver, solution of sa

nt that it can be washed, dried, and weighed without loss in handling. To secure these conditions it is essential that the current density (that is, the amount of current per unit of area of the electrodes) shall not

mployed, for a given electrode surface. The cause of the unsatisfactory character of the deposit is apparently sometimes to be found in the coincident liberation of considerable hydrogen a

gaseous chlorine molecules are formed and escape. The radicals which compose such ions as NO_{3}^{-} or SO_{4}^{-} are not capable of independent existence after disch

eparate the weights just indicated of the other substances. Experiments show that a current of one ampere passing for one second, i.e., a coulomb of electricity, causes the deposition of 0.001118 gram of silver from a normal solution of a silver salt. The number of coulombs required to deposit 107.94 grams is 107.94/0.001118 or 96,550 and the same number of coulombs will also cause the separation of 1.008 grams of hydrogen, 8 grams of oxygen or 31.78 grams of copper. While it might at first appear that Faraday's law could thus be used as a basis for the calculation of the time required for the

can be dried and weighed without change in composition. The platinum electrodes may be used in the form of dishes, foil or gauze. The last, on account of the ease of c

means of stirring the solution. With such an apparatus the amperage may be increased to 5 or even 10 amperes and depositions completed with great rapidity and accuracy. It is desirable, whenever practicable, to provide a rotating or stirrin

ION OF COP

dilute nitric acid (sp. gr. 1.20) and 5 cc. of water, heating gently, and keeping the beaker covered. When the sample has all dissolved (Note 2), wash down the sides of th

cooled in a desiccator and weighed. Connect the electrodes with the binding posts (or other device for connection with the electric circuit) in such a way that the copper will be deposited upon the electrode with the larger surface, which is made th

. Pass this current through the solution to be electrolyzed, and start the rotating mechanism. Keep the beaker covered as completely as possible, using a split watch-glass (or other device) to avoid loss by spattering. When the so

be increased to 0.2 ampere. The time required for complete deposition is usually from 20 to 24 hours. It is advisable to

aker, shut off the current, and, if necessary, complete the washing of the electrodes (Note 6). Rinse the electrodes cautiously with alcohol and heat them in a hot closet until the alcohol has just evaporated, but no longer, since

ght excess of ammonia. Compare the mixture with some distilled water, holding both above a white surface. The solution should not show any tinge of blue. If the presence

ight of copper on the cathode and of lead dioxide (PbO_{2}) on the anode

easily assured, when wire is used, by scouring with emery. If chips or borings are used, they

the solution to dryness, moisten the residue with 5 cc. of dilute nitric acid (sp. gr. 1.2) and add 50 cc. of hot water. Filter off the meta-stannic acid, wash, ignite in porcelain and weigh as SnO_{2}. T

r before using, and those portions upon which the metal will

t the cathode the Cu^{++} ions are discharged and plate out as metallic copper. This alone occurs while the solution is relatively concentrated. Later on, H^{+} ions are also discharged. In the presence of consider

be taken that the solution does not become al

ion as a result of the reducing action of the liberated hydrogen. Its re

NO{2} -> CO_{2} +

te free from the nitric acid solution before the cir

uit it is obvious that some device must be used to

may be cleaned by immersion in warm nitric acid. To remove the le

NATION

lly not over 0.1 per cent) which, unless removed, is

roxide which first forms re-dissolves, leaving only a slight red precipitate of ferric hydroxide. Filter off the iron precipitate, using a washed filter,

nited and weighed as ferric ox

centage of iron (

NATION

hould not be overstepped. Heat the solution nearly to boiling and pour into it slowly a filtered solution of di-ammonium hydrogen phosphate[1] containing a weight of the phosphate about equal to twelve times that of the zinc to be precipitated. (For this calculation the approximate percentage of zinc is that found by subtracting the sum of the percentages of the copper, lead and iron from 100 per cent.) Keep the

nt. It is advisable, therefore, to weigh out the amount of the salt required, dissolve it in a small volume of water, add a drop of phenolphth

per cent alcohol (Note 4). Dry the crucible and precipitate for an hour at 105°C., and finally to constant weight (Note 5). The filtrat

osphate (ZnNH_{4}PO_{4}) calculate the

e, necessary to precipitate the zinc in a nearly neutral solution, which is more accurately o

t becomes crystalline and then has the composition ZnNH_{4}PO_{4}. The precipitate then settles rapidly and

ng four hours. The ionic changes connected with the precipitation of the zinc as zinc ammonium phosphate are similar to those described for magnesium ammonium phosphate, exce

nt a slight decomposition of the precipitate (as a result of hydrolysis) if hot water alo

porcelain Gooch crucible within a nickel or iron crucible, used as a radiator. The heating must be

ll filter, dissolved in a few cubic centimeters of dilute nitric acid, and the zinc reprecipitated a

from this source may be avoided by determining the weight of the crucible and filter after weighing the precipitate. For thi

tion of zinc are fully discussed in an article b

N OF SILICA

r require fusion with an alkaline flux to effect decomposition and solution for analysis. The procedure given below applies to silicates undecomposable by acids, of which the mineral feldspa

ION OF T

he bolting cloth over the top of a small beaker in which the ground mineral is placed, holding the cloth in place by means of a rubber band below the lip of the beaker. By inverting the beaker over clean paper and gently tapping it, the

until the pieces are about half the size of a pea, and then transferred to a steel mortar, in which they are reduced to a co

s the bolting cloth, otherwise the sifted portion does not represent an average sample, the softer ingredients, if foreign matter is present, being first reduced to po

AND S

glazed paper, and thoroughly mix the substance and the flux by carefully stirring for several minutes with a dry glass rod, the end of which has been recently heated and rounded in a flame and slowly cooled. The rod may be wiped off with a small fragment of filter paper, which may be placed in the crucible. Place the remaining fourth of the carbonate on the top

ously prepared mixture of 100 cc. of water and 50 cc. of dilute hydrochloric acid (sp. gr. 1.12) in a covered casserole (Note

entages of silica, may require eight or ten parts by we

s decomposed by the alkaline flux. The sodium of the latter combines with the silicic acid of the silicate, with the evolution of carbon dioxide, while about two thirds of the

prevent a too violent reaction

icate to form a slightly ionized silicic acid. As a consequence, the concentration of the silicate ions in the solution is reduced nearly to zero, a

2}SiO_{3}), is a matter that is still debatable. It is certain, however, that the gelatinous material which readily separates from such solutions is of the nature of a hydrogel, that is, a col

-> [H_{2}SiO_{3}] -

e escaping carbon dioxide during the fusion. The crucible must therefo

decomposed. Such a residue should be filtered, washed, dried, ignited, and again fused with the alkaline flux; or, if the quantity of materia

ION AND

king sure that the acid comes into contact with the whole of the residue, dilute to about 200 cc. and bring to boiling. Filter off the silica without much delay (Note 2), and wash five times with warm dilute hydrochloric acid (one part dilute acid (1.12 sp. gr.) to three parts of water). Allow the filter to drain for a few moments, then place a clean beaker below the funne

mplishes this liberation. By disintegrating the fused mass with a considerable volume of dilute acid the silicic acid is at first held in solution to a large extent.

t require further treatment at this point. The progress of the dehydration is indicated by the behavior of the solution, which as evaporation proceeds usua

loric acid, and the solution freely diluted to prevent, as far as possible, the inclosure of the residual salts in the particles of

less an intermediate filtration of the silica occurs. If, however, the silica is removed and the filtrates are again evaporated and the residue heated, the amount

etter condition for filtration than when the lower temperature of the water bath is used. This, and many other points in the analysis of silicates, are fully di

curacy in the determination of silica, or of iron and alumina, it is also necessary to examine for silica the precipitate produced in the filtrate by ammonium hydroxide by fusing it with

hot water, the solution of these chlorides remaining in the filter after the passage of the original filtrate would gradually become so dilute as to throw down basic salts within the po

ND TESTING

need not be previously weighed, and burn off the filter (Note 1). Ignite for thirty minutes over the blas

then 3 cc. of hydrofluoric acid. !This must be done in a hood with a good draft and great

hood) until all the liquid has evaporated, finally igniting to redness. Cool in a desiccator, and weigh the crucible and residue. Deduct this

loc. cit.!) has shown that the silica holds moisture so tenaciously that prolonged ignition over the blast lamp is neces

d by volatilisation of the silica as silicon fluoride after solution in hydrofluoric acid, and, if the analysi

into contact with the skin, and its fu

The addition of the sulphuric acid displaces the hydrofluoric acid, and it may be assumed that the

to leave no residue on evaporation, a quantity equal to that employed in the

ly decomposable, it may be directly treated with hydrochloric acid, the solution evaporated to drynes

herwise the gelatinous silicic acid incloses particles of the original silicate and prevents decomposition. The water, by separating the particles and slight

sodium carbonate and a solution of the fused mass added to the original acid solution. This double procedure has an advantage, in that

RT

CHIO

ult to many students is due to the fact that, instead of understanding the principles which underlie each of the small number of types into which these problems ma

no less important than the manipulative skill required to obtain them, and that a moderate time spent in

wing: What is the factor for the conversion of a given weight of barium sulphate (BaSO_{4}) into an equivalent weight of sulphur (S)? The molecular weight of BaSO_{4} is 233.5. There is one atom of S in the molecule and the atomic weight of S is 32.1. The chemical factor is, therefore, 32.1/233.5, or 0.1375 and the weight of S corresponding to a given weight of BaSO_{4} is found by multiplying the weight of BaSO_{4} by this factor. If the problem takes the form, "What is th

3.6/159.6) and (3Mn/Mn_{3

hemical equivalents. It is plainly incorrect to express the ratio of ferrous to ferric oxide as (FeO/Fe_{2}O_{3}), since each molecule of the ferric

onversion of a given weight of ferrous sulphate (FeSO_{4}), used as a reducing agent against potassium permanganate, into the equivalent weight of sodium o

SO_{4} -> 5Fe_{2}(SO_{4}){3} +

2}SO_{4} -> 5Na_{2}SO_{4} + 10CO_{2}

react with 2KMnO_{4}. These molecular quantities are therefore equivalent, and the facto

iven weight of potassium permanganate (KMnO_{4}) into an equivalent weight of potassium bichromate (K_

SO_{4} -> 5Fe_{2}(SO_{4}){3} +

}SO_{4} -> 3Fe_{2}(SO_{3}){3} + K{2}

tiplied by 3 and the second by 5 the number of molecules of FeSO_{4} is then the same in both, and the number of molecules of KMnO_{4} and K_{2}Cr_{2}O_{7} reacting with these 30 m

ns, but it is usually possible to eliminate the common factors and solve but a single one. For example, the amount of MnO_{2} in a sample of the mineral pyrolusite may be determined by dissolving the mineral i

-> MnCl_{2} + 2

2KI -> I_

{2}O_{3} -> 2NaI

iosulphate solution used is known, what is the corresponding weight of manganese

O_{3}:I_{2}

_{2} = 2

nO_{2} =

{3}:MnO_{2} = 316.4:86.9, and the factor for the conversion of t

, and, as with the calculation of factors, to keep in mind the molecular relations between the reagent and the substance reacted upon. For example

Cl_{2}.2H_{2}O)

h, in turn, will require a molecule of the barium chloride for precipitation. To determine the quantity of the barium chloride required, it is necessary to include

paid to its specific gravity. For example, hydrochloric acid (sp. gr. 1.12) contai

alysis of silicate rocks, the sodium and potassium present may be obtained in the form of their chlorides and weighed together. If the weight of such a mixture is known, and also the percentage of chlo

y 0.15 x 0.53, or 0.0795 gram. Let x represent the weight of sodium chloride present and y that of potassium chl

.5/58.5)x + (35.

ght of NaCl to be 0.0625 gram. The weight o

noted that the results obtained by these indirect methods cannot be depended upon for high accuracy, since slight errors in the determination of the common constituent, as chlorine in

OB

this by 1 when the second decimal is 5 or above. Thus, 39.1 has been taken as the atomic weight of potassium, 32.1 for sulphur, etc. This has been done merely to secure uniformity of treatment, and the student should remember that it is always well to take into account the degree of accuracy desi

TRIC A

hydroxide are required for exactly

!: 56.1

id as an acid; (b) of hydrochloric acid as an acid; (c)

49.05; (b) 36.5

droxide; (b) of sodium carbonate; (c) of barium hydroxid

6.1; (b) 53.8; (

ams of Na_{2}HPO_{4} (a) as a p

(a) 47.33

ns 23.81 per cent hydrochloric acid by weight. Calculate the grams and the millieq

67 gram; 7.307

gr. 1.20 containing 39.80 per cent HCl by weight) are

r!: 76

equivalents of hydrochloric acid i

r!: 0.

rochloric acid are exactly equivalent to 1.216 grams of pure sodium carbonate, usi

r!: 0.

l hydrochloric acid to the equivalen

r!: 22

1 normal sulphuric acid and 50 cc. of exactly normal potassium hydroxide added from a pipette. Is the solution acid

cc. alkali (sol

to be 0.5172. Of this acid 39.65 cc. are exactly equivalent to 21.74 cc

r!: 0.

ain 92.44% CaCO_{3} and no other basic material. The sample weighing 0.7423 gram was titrated by adding an excess of acid (42.42 cc.) and titrating th

d 0.4398 N; al

arbonate (Na_{2}CO_{3}) will be neutralized by a portion of it? (c) how many grams of silver will there be in the silver chloride formed when an excess of silver nitrate is added to a portion? (d) how many grams of iron will

0.053; (c) 0.1079; (d) 0.02

ssolved and the solution diluted to exactly 1 liter, and 40 cc. are neutralized with 20 c

r!: 0.

ssium hydroxide; (b) to neutralize 30 cc. of 0.5 normal barium hydroxide; (c) to neutralize 20 cc. of a solution contain

; (b) 50 cc.; (c) 66.

uivalent to 0.1027 gram of pure sodium carbonate to make it exactly 1.250 nor

r!: 10

. HCl. The HCl is 0.4876 N. How much water must be add

er!:

cid solution which has a specific gravity of

r!: 35

o convert it to the double carbonate, is titrated with sulphuric acid, using methyl oran

le = 0.9

4} used =

sed =

SO_{4} = 1.

lue NaOH

r!: 87

, and 17.36 cc. of 1.075 N acid is added. Is the resulting solution acid or alkaline? How many cubi

Acid; 1.86

tly 46.32 grams of pure KOH and 27.64 grams of pure NaOH, and after dissolving in water, diluted the solution to exactly o

r!: 74

ammonia liberated is distilled and collected in 50 cc. of 0.5 N acid and the excess titrate

er!:

ethyl orange, the color change takes place only when the carbonate has been completely neutralized. From the following data, calculate the percentages of Na_{2}CO_{3} and NaOH in an impur

7% NaOH; 84.28

acid, using phenolphthalein in cold solution as an indicator and becomes colorless after the addition of 48.16 cc. Meth

50% NaOH; 64.9

00 gram; volume of 0.25 N hydrochloric acid required for phenolphthalein end-point, 26.40 cc.; after adding an excess of acid a

Na_{2}CO_{3}; 3

e normality of the acid in order that the number of cubic centimeters

!: 0.45

order that the number of cubic centimeters of 0.5 N acid us

!: 1.15

_{4}H_{4}O_{6} in an analysis involving the following data: NaOH used = 30.06 cc.; H_{2}SO_{4} solution u

!: 2.84

ollowing data: Weight of sample = 1.00 gram; HCl sol. used = 55.90 cc.; NaOH sol. used = 0.42 cc.; 1

er!:

ght of H_{2}C_{2}O_{4}.2H_{2}O = 0.2460 gram; NaOH solution used = 41.03 cc.; HCl solution used = 0.63; 1 cc. NaOH so

er!:

cid are equivalent to 43.76 cc. of the NaOH solution. The NaOH is standardized against a pure potassium tetroxalate (KHC_{2}O_{4}.H_{2}C_{2}

er!:

id must be added to 300 cc. of 0.4 N phosphoric aci

er!:

uires 3 cc. of a given solution of HNO_{3}. What is the normality of the nitric acid when

r!: 0.

ple of dolomite, by adding an excess of hydrochloric acid, as can be liberated by the addition of 35 cc. of 0.5 N

er!:

ill be required to displace the chloride in the calcium chloride formed by the action of 100 cc. of 0.1

0.298 cc.;

d 90% KOH. What weight of residue will be obtained if one gram of this sample is added to 46 cc. of normal hydrochloric acid

!: 3.47

at they contained either pure NaOH; pure Na_{2}CO_{3}; pure NaHCO_{3},

in to a solution of the substance

.26 cc. for a change in color, using phenolphthalein, and

d until the pink of phenolphthalein disappeared, and on t

, 15.00 cc. were required. A new sample of the same weight required e

3}; (b) NaHCO_{3}+Na_{

2}CO

732 gram. NaOH solution used = 24.97 cc. 3.00 cc. NaOH = 1 cc. of H_{3}PO_{4} solution of which 1 cc. wil

er!:

oric acid, using methyl orange as an indicator, requires 38.60 cc. for complete neutralization. Barium chloride in excess is added to a second portion of 100 cc. of the solution, which is diluted to exactly 250 cc., allowed to

aOH; 4.45% Na_{2}CO

so that it was supposed to contain 15% of A, on the basis of the analyst's report. Owing to the carelessness of the analyst's assistant, the sodium hydroxide solution was used with phenolphthalein as an indicator in cold solution in making the analyses. The concern manufacturing this material sells 600 tons per year, and when

lost; 3.94% Na_{2}

ere added. The weight of the wire used was 0.22 gram. 3.27 cc. of a ferrous sulphate solution having a normal value a

r!: 0.

d be taken to standardize an approximately 0.1 N oxid

!: 0.46

ith bromine water. How many grams of stannous chloride are there in a liter of solution if it requires 9.47 cc. to

17.92 gram

iron is reduced with stannous chloride, mercuric chloride is added, and the iron titrated with a normal K_{2}

!: Fe_{

O_{4}^{-} anion, compute the oxide, or valence, corresponding to the reduced state from the following data: 0.3266 gram of the pure element, after being di

!: Mono

owing data: Sample = 0.5000 gram. KMnO_{4} used = 50 cc. 1 cc. KMnO_{4} =

er!:

Al_{2}O_{3} and the iron present requires 25 cc. of 0.2 N KMnO_{

89% FeO; 10.0

%; magnesium oxide, 20.70%; carbon dioxide, 43.00%. In manufacturing lime from the above the carbon dioxide is reduced to 3.00%. How m

r!: 20

d 75 cc. of ferrous sulphate solution (80 grams FeSO_{4}.7H_{2}O per liter) are mixed, and the resulting solution tit

r!: 5.

{3} requires 40 cc. of KMnO_{4} to oxidize the iron, what is the value of

.005189 gram; (b

xalic acid. The excess oxalic acid requires 23.95 cc. of permanganate (1 cc. = 0

er!:

{2}O_{4}.2H_{2}O per liter. What is the normal value of

a) 0.5903 N;

with sulphurous acid. On account of failure to boil out all the excess SO_{2}, 38.60 cubic centimeters of 0.1 N KMnO_{4} were

.60%; (b) 2.67%;

o the tetroxalate solution as a reducing agent: 1 cc. HNO_{3} = 1.246 cc. NaOH solution; 1

er!:

itate weighing 0.5465 gram. 24.35 cc. of the hydrochloric acid are exactly equivalent to 30.17 cc. of KHC_{2}O_{4}.H_{2}C_{2}O_{4}

r!: 55

H_{2}O) are dissolved in water and diluted to exactly 1000 cc. The normal value of the oxalate solution when used as an acid is 0.1315.

!: 2:1;

r to be 0.07500 N as an alkali and the latter exactly 0.1 N as an oxidizing agent. By coincidence, exactly 47.26 cc. were used in each

wer!

ecipitated as (NH_{4}){3}PO{4}.12MoO_{3}, and the precipitate (after solution and reduction of the MoO_{3} to Mo_{2

er!:

the yellow precipitate was dissolved, reduced and titrated with KMnO_{4}. If the sample contained 0.025 per cent P and 6

!: Mo_{

e solution (1 cc. equivalent to 0.0300 gra

: 0.0093

otassium iodide solution by 0.3000 gram of pure KIO_{3}. (KIO_{3} + 5KI + 3H_{2}SO_{4} = 3K_{2}SO_{4} + 3I_{2} +

0.1753 N; 0

t of the thiosulphate is decomposed by the carbonic acid present in the solution. To what volume must the solution be

r!: 10

ich 1 cc. is equivalent to 0.004950 gram of As_{2}O_{3}. Due to an error on his part in standardization, the student's analysis show

: 0.1000

ine is titrated with sodium thiosulphate solution (49.66 grams of pure Na_{2}S_{2}O_{3}.5H_{2}O per liter). If 38.72 cc. are required, what volume of 0.25 normal permangana

r!: 26

chloride solution, and decomposing the CdS with acid in the presence of a measured amount of standard iodine, the following data are obtained: Sample, 5.027 grams; cc. Na_{2}S_{2}O_{3} sol.

er!:

= 2HCl + 2FeCl_{2} + I_{2} is reduced by the addition of 50 cc. of sodium thiosulphate solution and the excess thiosulphate is titrated with standard iodine and requires 7.8

er!:

{2} solution, the acidified precipitate being titrated with iodine and thiosulphate. Sample, 5.076 grams; cc. I_{2} = 20.83; cc. Na_{2}S_{2}O_{3} = 12.37; 43.45 cc. Na_{2}S_{2}O_{

er!:

ze the same amount of oxalic acid as 37.12 cc. of a permanganate s

!: 0.24

iodine liberated from KI by the manganese dioxide is sufficient to react with

r!:: 0

m sample, what is the least normal value that a potassium thiocyanate solu

r!: 0.

5 cubic centimeters of 0.2017 N silver nitrate, and the excess titrated with 25 cc. of 0.1 N KSC

er!:

1500 gram, and after solution in water requires 22.71 cc. of 0.1012 N silver nitrate for the pr

24% Na_{2}O;

ETRIC

carbon dioxide liberated by the addition of an excess of acid to one gram of calcium

0.7526; (b) 0.4

(b) MgO in Mg_{2}P_{2}O_{7}; (c) P_{2}O_{5} in Mg_{2}P_

(b) 0.3620; (c) 0.6378;

PbCrO_{4}; (b) Cr_{2}O_{3} in PbCrO_{4}; (c

0, (b) 9.3713-10; (c) 9

_{3}O_{4} can be obtaine

!: 0.87

AgCl weighing 0.2991 gram, what weight of AgI could have been obtained from

0.4898 gr

aining 25.75% HCl by weight) are required to exactly neutralize 25 cc.

r!: 47

H_{3} by weight) are required to precipitate the aluminium as aluminium hydroxide from a two-g

2.26 cc.; 0

required to oxidize the iron in one gram of FeSO_{4}.7H_{2}O in the presence of sul

r!: 0.

. 1.11 containing 21.92% HCl by weight) is added, how many cubic centimeters of ammonia (sp. gr. 0.96 contain

r!: 2.

.90 containing 28.4% NH{3} by weight). How many cubic centimeters of sulphuric acid (sp. gr. 1.18 containi

r!: 34

s SO_{2} per liter) are required to reduce the iron in 1 gram of ferric alum (KFe(

r!: 0.

ng 26.30 grams of K_{2}Cr_{2}O_{7} per liter must be taken in order to yield

3SO_{2} + H_{2}SO

O_{4}){3

r!: 44

precipitate the iron as Fe(OH){3} from a sample of pure FeSO{4}.(NH_{4}){2}SO{4}.6H_{2}O, which requires 0.34 cc. of nit

r!: 4.

(OH){3}, what weight of sample must be taken for analysis so that each one hundredth of a gra

!: 6.99

taken for analysis so that the number of centigrams of BaSO_{4} obtai

!: 0.68

ting and igniting all the iron to Fe_{2}O_{3}, the percentage of Fe_{2}O_{4} in the sa

!: 0.96

esia mixture" (MgCl_{2} + 2NH_{4}Cl). If exactly 12.6 cc. of the mixture are required, how many grams of MgCl_{2}

!: 30.7

gram of the sample gives 0.4013 gram of Mg_{2}P_{2}O_{7}, how many cubic centimeters of ammonium oxalate solution (containing

r!: 25

e, when treated with an excess of hydrochloric acid, yields 0.3117 gram of carbon dio

ium oxalate and ignited to calcium oxide. What volume of gas, measured over water at 20°C. and 765 mm. pressure, is giv

er!:

ight of CaO obtainable from 3 tons of the limestone, assuming complete conversion to oxide

1.565 tons;

ct is assumed to be CaO and the analyst reports 29.50% Ca in the sample. Owing to insufficient ignition, the product actually co

28.46%; 3

at the volume in cubic centimeters of CO_{2} obtained by treating with acid, me

!: 0.23

red to dissolve 5 grams of brass, containing 0.61% Pb, 24.39% Zn, and 75% Cu, assuming reduction of t

!: 55.06

alt solution by a current of 1.5 amperes during a period of 45 minut

!: 1.33

}, and a deposit of metallic copper exactly equal in weight to the ignited precipitate of Zn_{2}P

75% Cu; 29.92%

olved in nitric acid. The lead is determined by weighing as PbSO_{4}, the copper by el

. gr. 1.42 containing 69.90% HNO_{3} by weight) requir

r!: 2.

uric acid (sp. gr. 1.84 containing 94% H_{2}

r!: 0.

e the weight

!: 0.01

9640 grams. Calculate the weight a

: 11.611

4}){2}HPO{4} required to precipi

!: 0.57

weight of ignite

!: 0.65

out, what percentage error in the zinc determination would result? What volume of a solution of sodium hydrogen phosphate, containing 90 grams o

% error; (b) 39.97

and loses 0.1000 gram on ignition. What volume of disodium phosphate solution (containing 90 grams Na_{2}

r!: 9.

solve a sample of brass containing 69.27% Cu; 0.05% Pb; 0.07% Fe; and 30.61% Zn. Assuming the acid used as oxidizing a

0.992 gram

nd silver bromide is found to contain 0.6635 gr

er!:

current of chlorine, the silver bromide is converted to silver chloride, and the mixture lo

er!:

0.6460 gram. This is fused with 4 grams of sodium carbonate. How many grams of the carbonate actually co

.135 grams;

rams is transformed into mixed sulphates, weighing 5.023 grams. Ca

24 grams CaO;

PE

IC DISSOCI

n in the Notes accompanying the various procedures. The reader who desires a more extended discussion of the fundamental theory and its uses is referred to such books

ups of atoms, as, for example, H^{+} and Br^{-} from hydrobromic acid, Na^{+} and OH^{-} from sodium hydroxide, 2NH_{4}^{+} and SO_{4}^{-} from ammonium sulphate. The unit charge is that which is dissociated with a hydrogen ion. Those upon other ions vary in sign and number a

on, be balanced by a corresponding negative charge on some other ion. When an electric current is passed through a solution of an electrolyte the ions move with and convey the current, and when the cations come into contact

ferent properties. For example, the ion MnO_{4}^{-} from permanganates yields a purple-red solution and d

of the ions. The percentage dissociation of the same electrolyte tends to increase with increasing dilution of its solution, although not in direct proportion. The percentage dissociation of different electrolytes in solutio

C

========================

PERCENTAGE D

UIVALENT

_____________________|__

, HI, HN

ClO_{4}, HM

-> H^{+} + HS

<-> H^{+} + HC_{

-> H^{+} + HS

H^{+} + H_{2}

<-> H^{+} + HP

> H^{+} + H_{2}

|

_{3}O_{

> H^{+} + HCO_

H^{+} + H

|

========================

A

========================

PERCENTAGE D

UIVALENT

_____________________|__

NaO

H){2

}OH

========================

A

========================

| PERCENTAGE

UIVALENT

_____________________|__

R^{-}

R^{-}){

){2}R^

}R^{-

========================

cal conductivity of the solutions and by other physico-chemical m

are largely dissociat

nd is measured by the percentage dissociation in solutions of equivalent concentration. The common mineral acids are largely dissociated and therefore give a relati

ir relative dissociation in solutions of equivalent concentration. Ammonium hydroxide is a weak base, as

ese changes it is necessary to consider first the conditions which prevail when a solution of acetic acid, which has been stirred until it is of uniform concentration throughout, has come to a constant temperature. A careful study of such solutions has shown that there is a definite state of equilibrium between the constituents of the solution; that is, there is a definite relation between the undissociated acetic acid and its ions, which is characteristic for the prevailing conditions. It is not, however, assumed that this is a condition of static equilibrium, but rather that there is continual dissociat

C_{2}H_{3}O_{2}^{-})/C

sta

en the product of the concentrations of the ions and the concentrat

substances taking part in the reaction; or, if conditions of equilibrium are considered in which, as stated, the rate of change in opposite directions is assumed to be equal, then the product of the concentrations of the substances e

the temperature remains constant. If the temperature changes the value of the constant changes somewhat, but is agai

========================

|

LAL CONCENTRA- | MOLA

| TION OF H^{+} AND| T

ETATE^{-} IONS

_|__________________|___

|

| .004 | .9

|

.0013 | .09

|

.000407 | .00

|

=========================

Smith, !General Inorgan

_{2}^{-} ions per liter which would result from the complete dissociation of a gram-molecule of acetic acid. The values calculated for the constant are subject to some variation on account of

e addition of water the conditions of concentration which led to equality in the rate of change, and hence to equilibrium in the molal solution, cease to exist; and since the dissociating tendency increases with dilution, as just stated, it is true at the first instant after the addition of water that th

applications of the ionic theory in analytical chemistry, and it should be clearly understood that whenever an existing state of equilibrium is disturbed as a result of changes of dilution or temperature, or as a consequence of chemical changes which bring into action any of the constituents of the solution, thus altering their concentrations, there is always a tendency to re-establish

the silver nitrate is AgNO_{3} <-> Ag^{+} + NO_{3}^{-}, and as soon as the Ag^{+} ions unite with the Cl^{-} ions the concentration of the former is diminished, more of th

exactness in these cases is not known, the law is still of marked service in developing analytical methods along more logical lines than was formerly practicable. It has not seemed wise to qualify each statemen

quantitative analysis, we derive what is known as the !solubility product!, as follows: Taking silver chloride as an

onc'n Cl^{-})/Conc'

tant for that temperature. Since it is a constant, it may be eliminated, and the expression becomes !Conc'n Ag^{+} x Conc'n Cl^{-} = Constant!, and this is known as the solubility product. No precipitation of

eased, and as a result the concentration of the other ion must proportionately decrease, which can only occur through the formation of some of the undissociated compound which must separate from the

on, as, for instance, the addition of hydrochloric acid to a solution of hydrogen sulphide. Hydrogen sulphide is a weak acid, and th

d, displaces the point of equilibrium and some of the S^{-} ions unite with H^{+} ions to form undissociated H_{2}S. This is of much importance in studying the reactions in which hydrogen sulphide is employed, as in qualitativ

he action of hydrochloric acid upon magnesium hydroxide. The minute quantity of dissolved hydroxide dissociates thus: Mg(OH){2} <-> Mg^{++} + 2OH^{-}. When the acid is introduced, the H^{+} ions of the acid unite with the OH^{-} ions to form undissociated water. The concentration of the O

acid being less dissociated than normally in the presence of the H^{+} ions from the hydrochloric acid (see statements regarding hydrogen sulphide above). As the undissociated oxalic acid forms, the c

for example, when dissolved in water gives an alkaline solution because some of the H^{+} ions from the water unite with CN^{-} ions to form (HCN), which is a very weak acid, and is but very slightly dissociated. Potassium hydroxide, which might form from the OH^{-} ions, is so largely dissociated that the OH^{-} ions remain as such in the solution. The union of the H^{+} ions with the CN^{-} ions to form the undissociated HCN diminishes the concentration of

d is strong and the base weak, and the OH^{-} ions form the little dissociated Al(OH){3}, while the H^{+} ions rem

in analytical chemistry, especially in the understanding of t

rmed !electrolytic solution pressure!, or ionization tension. This force may be measured in term

less solution pressure when placed in a solution of its salt, as, for instance, when a strip of zinc

with reference to the other common elements. For a more extended d

SERIES OF

-0.13 Calcium Ca^{++} | | Hydrogen H^{+} | -0.28 Magnesium Mg^{++} | | Bismuth Bi^{+++}| Aluminum A1^{+++} | +1.00 | Antimony | -0.75 Manganese Mn^{++} | | Arsenic | Zinc Zn^{++} | +0.49 | Copper Cu^{++} | -0.61 Cadmium Cd^{++} | +0.14

NG OF A F

s for analytical use are supposed to have the same angle, but are rarely accurate. It is possible, however, with care, to fit a filter thus folded into a funnel in such a way as to p

as follows: (1) Fold the filter evenly across one of the diameters, creasing it carefully; (2) open the paper, turn it over, rotate it 90° to the right, bring the edges together and crease along the other diameter; (3) open, and rotate 45° to the right, bring edges together, and crease evenly; (4) open, and rotate 90° to the right, and crease evenly; (5) open, turn the filter over, rotate 22-(1/2)° to the right, and crease evenly; (6) open, rotate 45° to the right and crease evenly; (7) open, rotate 45° to the right and crease evenly; (8) open, rotate 45° to the right and crease evenly; (9)

S FOR LABORA

ag

a

ION OF B

_________________________

|

E | OBSERVED | DIFF

| WEIGHTS |

_____|______________|____

| 16.

0 | 26.35 |

7 | 36.26 |

7 | 46.34 |

03 | 56.31

1 | 66.17 |

_____|______________|____

btained in duplica

ag

a

COMPARATIVE STR

_________________________

NATION

|________________________

cted |

Cl | 48.17 48.0

ng HCl | 0.12

--- |

96 |

cted |

Cl | 46.36 46.2

ng HCl | 1.75

--- |

54 |

OH | 1.646

HCl | 8.31

--

- 10 | 9.

290 cc. NaOH |

| .

|________________________

gn

ag

a

ION OF HYDRO

=======================

and tube| 9.

731 |

--

ple | 1.00

Cl | 39.97 39.8

ng HCl | .00

--- |

83 |

g NaOH | .26

ng NaOH | .12

-- |

14

14

39.83 - --- = 39.68

86 |

e | 0.002

.4014 - 10 |

quivalent| 1.

--

- 10 | 9.

ue HCl | .

| .

=======================

gn

ag

a

CHLORINE IN CHL

=======================

and tube| 16

976 |

-- |

mple | .1

cruci

te | 14.449

ghts | 14.44

4.4

ible | 14.2

ight | 14.2

Cl | .226

1.5496

l | 9.3558 - 1

| 2.0000

7.8438 - 10

le | 0.758

-- |

075 |

e No. | 32.

=======================

gn

TH OF

n the procedures described in the foregoing pages. It is obvious, ho

x. Ap

elation

normal

olution

NH_{4}){2}C{2}O_{4}

, BaCl_{2}.2H_{

chloride (of MgCl

ride, HgCl_{2

oxide, KOH (sp

ocyanate, KSC

e, AgNO_{3} 2

oxide, NaOH

ate. Na_{2}CO

_{2}HPO_{4}.12H_{2}O

.2) with tin, diluting with an equal volume of water, and adding a slight ex

f concentrated ammonium hydroxide (sp. gr. 0.90). Filter, and pour the filtrate slowly, with constant stirring, into a mixture of 400 cc. concentrated nitr

the Standard Tables of the Manufacturing Chemists' Association of the United States [!J.S.C.I.!, 24

9.91 per cent NH_{3} by weight, and corr

8.52 per cent NH_{3} by weight, and corre

s 23.81 per cent HCl by weight, and corr

39.80 per cent HCl by weight, and corres

5 per cent HNO_{3} by weight, and corres

6 per cent HNO_{3} by weight, and corres

.19 per cent H_{2}SO_{4} by weight, and cor

74 per cent H_{2}SO_{4} by weight, and cor

ce as in volumetric analyses. The molal solution is assumed t

S OF WATER AT TEMPER

re Densit

tig

001571 20° 0.998230 1.001773 21° 0.998019 1.001985 22° 0.997797 1.002208 23° 0.997565 1.002441 24° 0.997323 1.002685 25° 0.9

tein, and Meyerhoffer's !

NGE OF TEMPERATURE

s, except in the comparatively few cases where the highest attainable accuracy is demanded in chemical investigations. The expansion coefficients should then be

ions fo

on. of solu

and

al .

ormal

more dilute so

ution varies from the standard temperature selected for the laboratory. The total correction thus found is subtracted from the observed burette reading if

ONAL ATOM

===================

0 | |

________|__________

27.1 | Molybd

120.2 | Neodym

39.9 | Neo

74.96 | Nic

37.37 | Nitro

208.0 | Osm

1.0 | Oxyge

79.92 | Palla

12.40 | Phosph

132.81 | Plat

40.07 | Potas

005 | Praseody

140.25 | Rad

35.46 | Rhod

52.0 | Rubid

8.97 | Ruthen

| 93.1 | Sama

63.57 | Scan

| 162.5 | Sele

167.7 | Sili

152.0 | Silv

| 19.0 | Sod

| 157.3 | Stro

69.9 | Sulp

| 72.5 | Tant

9.1 | Tellur

7.2 | Terbiu

4.00 | Thall

1.008 | Thori

114.8 | Thul

126.92 | Ti

193.1 | Titan

.84 | Tungst

82.92 | Ura

| 139.0 | Van

07.2 | Xeno

6.94 | Ytterb

| 175.0 | Yt

| 24.32 | Z

54.93 | Zirco

Hg | 2

===================

N

dim

lutions

an

defin

action of o

of sa

acy d

ali

olutions

an

ermination o

m nitra

hemistry, su

ermination of

e, ana

tos f

eights,

lphur in Bases, definition of Bichromate process for iron Bleaching powder, analysis

rmination of,

ion, def

bur

fla

determination

ori

avimetric de

on ore, a

rmination

olution of

analyses, d

ermination

ion of in

bles,

ine prec

ies of

ion pot

icc

ct m

ation,

my of

dissociatio

separations,

t, defin

rium, c

tion of

day'

r, anal

nium sulphat

s, fol

fi

es, tes

tra

gradua

nn

moval of fr

ions for gravi

tric a

h fi

analysis,

acid, stand

rol

ndirect methods Insoluble matter, determination of in limestone Integrity Iodimetr

s re

rmination

ne, ana

eterminatio

, evapo

nsf

tm

ari

, determi

ction,

ng inst

yl o

ermination of

s, acid and alkali oxidizing agents re

determination

ion pr

power of

f description of Platinum crucibles, care of Precipitates, colloidal crystalline ignition of separation fro

Analyses, s

s, stre

solutio

tor,

ible r

rmination of

ion of, in

icati

cid, dehy

terminatio

alkaline s

, determination

lity p

ion p

ions,

an

ation, def

ons, acidimetry

ori

ime

and redu

ocy

h sol

termination

ring

chio

th of

on, u

tion of in ferrous

ium su

re, corre

g of w

lectrolytic

e process

n, defin

er of

analysis, d

l dire

-bot

ed f

of pre

gs, te

ioniz

itie

ts, c

einhardt met

rmination