tion of the bismuth is either determined from the loss of weight which the analysed substance suffers, or the volatilized chloride of bismuth is conducted into water impregnated with hydrochloric acid, and subsequently determined according to § 91.

7. Separation by means of metallic lead.

The solution is precipitated with carbonate of ammonia; the precipitated carbonates are washed, and subsequently dissolved in acetic acid. The solution is introduced into a flask provided with a ground stopper, a weighed rod of pure lead is placed upright into the solution, and the flask nearly filled with water, so that the upper end of the lead does not project beyond the surface of the fluid; the flask is then closed, and allowed to stand at rest for the space of twelve hours, with occasional agitation. The bismuth which precipitates upon the metallic lead, is rinsed off from the rod, and collected upon the filter; it is then washed, and dissolved in nitric acid; the solution is evaporated, and the bismuth determined as directed § 91. The lead in the filtrate is determined according to § 87; the lead-rod is dried, and re-weighed; the loss of weight which it has suffered in the process, is subtracted from the amount of lead produced from the filtrate. (Ullgren.)

14. OXIDE OF LEAD FROM THE OXIDES OF COPPER

AND CADMIUM.

a. Separation by means of cyanide of potassium.

Like oxide of lead from oxide of silver. (§ 127, 2, B.)

B. Separation by means of sulphuric acid.

Like oxide of lead from peroxide of mercury. (§ 127, 7, y.) 15. OXIDE OF BISMUTH FROM OXIDE OF COPPER.

a. Separation by means of cyanide of potassium.

Like oxide of lead from oxide of copper. (§ 127, 14.)

B. Separation by heat.

Like mercury from copper, § 127, 6; compare likewise § 127, 13, B. This method is especially applicable in the case of alloys. 7. Separation by means of ammonia.

The solution is mixed with sal ammoniac, and then gradually

dropped into dilute ammonia. This causes the bismuth to precipitate as a basic salt, whilst the oxide of copper remains in solution as an ammoniacal double salt. (BERZELIUS.) The precipitate is washed with dilute ammonia, dissolved in dilute nitric acid, and the bismuth in the solution determined according to the directions given § 91. The copper in the ammoniacal solution is determined as directed § 90, 1, a., B.

16. OXIDE OF BISMUTH FROM OXIDE OF CADMIUM. The separation is effected by means of cyanide of potassium, like that of oxide of lead from oxide of cadmium; vide § 127, 14, a.

17. OXIDE OF COPPER FROM OXIDE OF CADMIUM.

The separation is effected by means of cyanide of potassium, in the same manner as that of oxide of silver from oxide of copper; vide § 127, 4, ẞ, aa.

18. ALL THE METALS OF THE FIFTH GROUP FROM ONE

ANOTHER.

The dilute solution is mixed with carbonate of potass, and subsequently with cyanide of potassium in excess; the mixture is digested for some time, at a gentle heat, and filtered. The carbonates of lead and of bismuth (mixed with alkali) remain upon the filter; the lead is separated from the bismuth as directed § 127, 13. The filtrate is mixed with dilute nitric acid in excess, and the fluid filtered off from the precipitated cyanide of silver, which is to be determined according to § 86, 3. The filtrate is again neutralized with carbonate of potass; cyanide of potassium is then added, and sulphuretted hydrogen in excess transmitted through the solution; a fresh portion of cyanide of potassium is then added-(to re-dissolve every trace of sulphuret of copper which may perchance have been precipitated)—and the solution which contains all the copper, filtered off from the precipitated bisulphuret of mercury and sulphuret of cadmium, which are finally separated from one another, as directed § 127, 10. The copper in the filtrate is determined according to § 127, 4.

TIN-PEROXIDE OF TIN- OXIDE OF ANTIMONY -ARSENIOUS ACID-ARSENIC ACID.

I. SEPARATION OF THE OXIDES OF THE SIXTH GROUP FROM THOSE OF THE FIRST FOUR GROUPS.

§ 128.

a. Separation of all the oxides of the sixth group from those of the first four groups.

a.

Sulphuretted hydrogen in excess is conducted into the acid solution, and the precipitated sulphurets (corresponding to the oxides of the sixth group) are filtered off.

The points mentioned § 126, a., a and y are here to be likewise attended to. With regard to the particular conditions requisite to effect the complete precipitation of the individual metals of the sixth group, I refer to section IV. Wöhler has found that sulphuretted hydrogen fails to separate arsenic acid from oxide of zinc, even though a considerable excess of mineral acid be present, since the whole, or a portion of the zinc, will invariably precipitate in conjunction with arsenic: Zn S, As S. In cases, therefore, where we have oxide of zinc and arsenic acid together in solution, the arsenic acid must first be converted into arsenious acid, by heating with sulphurous acid, before the sulphuretted hydrogen is transmitted through the solution.

B. It is more convenient in some cases to base the separation of the metals of the sixth group from those of the third and fourth groups, upon the solubility of the sulphurets of the former in alkaline sulphurets, since neither the hydrates of alumina and oxide of chromium, nor the sulphurets of the metals of the fourth group, are dissolved by alkaline sulphurets. The process is, in such cases, conducted as directed § 129, a, B. This method is not applicable in cases where the compound to be analysed contains nickel.

b. Separation of individual oxides of the sixth group from those of the first four groups.

1. GOLD.

a. Metallic gold may be readily separated from the metals of the fourth group, by means of nitric acid or hydrochloric acid, since these acids dissolve the other metals, and leave the gold intact.

B. If we have peroxide of gold in acid solution, together with the oxides of the four first groups, the gold may be readily precipitated with oxalic acid, (§ 93,) and thus separated from the other oxides. Care must be taken to add a sufficient amount of hydrochloric acid to the solution, lest oxalates insoluble in water should precipitate in conjunction with the gold, owing to a deficiency of their proper solvent.

2. PLATINUM may be separated from all those metals of the four first groups, of which the chlorides dissolve in alcohol, by precipitating it with sal ammoniac, according to § 94. Compare likewise the separation of platinum from the metals of the fifth group, 129, 5.

3. TIN AND ANTIMONY.

a. These metals may be separated from their alloys with metals of the fourth group, by means of nitric acid, since this leaves the oxides of tin and antimony which are formed, undissolved, whilst it dissolves the other oxides. (The results are not perfectly accurate, especially in the case of antimony, of which a small portion is dissolved in the process.)

B. Tin and antimony may be readily separated from those metals of which the chlorides are fixed, by heating the mixed metals in a stream of chlorine gas; compare § 127, 1, 7. The volatilizing chloride of antimony and chloride of tin are to be conducted into water impregnated with hydrochloric acid.

4. ARSENIC may, under certain circumstances, be advantageously separated from the oxides of the fourth group, &c., by the method which will be found described § 129, 7, a. This method is not applicable, however, for the separation of the acids

of arsenic from alumina. From barytes, strontia, and lime, arsenic acid may be readily separated by means of sulphuric acid. In the case of strontia and lime, alcohol is added, to separate the precipitates completely from the fluid. The best way is, to dissolve the compound to be analysed in hydrochloric acid before adding the sulphuric acid; should the compound be insoluble in hydrochloric acid, it is to be reduced to a very fine powder, boiled for some time with concentrated sulphuric acid, and the further process conducted as stated above. The proportion of the arsenic acid may be calculated from the loss of weight which the analysed compound undergoes, or it may be determined in the filtrate by means of sulphuretted hydrogen.

Arsenite of barytes may be decomposed immediately by sulphuric acid, but the arsenites of strontia and lime must first be converted into arseniates by repeated evaporation with nitric acid and cautious ignition.

II. SEPARATION OF THE OXIDES OF THE SIXTH GROUP FROM THOSE OF THE FIFTH.

§ 129.

a. Separation of all the oxides of the sixth group from those of the fifth.

The sulphurets of the sixth group are soluble in alkaline sulphurets, whilst those of the fifth group are insoluble in these reagents. This furnishes us with a ready means of separating the metals of the fifth from those of the sixth group. Sulphuret of ammonium is generally used as the solvent; if protosulphuret of tin is present, the sulphuret of ammonium must contain sulphur in excess, or a certain amount of sulphur must be added to it. If copper is present, sulphuret of potassium is to be substituted for ammonium, since sulphuret of copper is slightly soluble in the latter; this substitution, however, is admissible only if no mercury is present, since the sulphurets of