freely during four or five minutes by the m tube, and all the air originally contained in been expelled, light the gas issuing from the tube, and pour into the thistle-tube, a portion mixture of strong chlorhydric acid and the resi antimony and tin, or the solution if the acid the residue completely. Hold a cold porcela flame, taking care to shift the position of the d so that fresh surfaces of porcelain may be ex burning gas. If there be really any antimony ble residue, antimoniuretted hydrogen will b gether with free hydrogen, and characteristic sm black spots or stains of metallic antimony w deposited from it upon the cold porcelain. T sure that the spots are really composed of anti of arsenic, cover them with a solution of blea (hypochlorite of calcium); if they are antimo will not dissolve, while arsenic spots dissolve at pare Eliot and Storer's Manual, pp. 270, 271.

In order not to explode the test-tube on lig the operator must wait patiently for several all the air has been expelled from the tube.

The whole of the antimony is not converted into antimoniuretted hydrogen; a portion is metallic state, and if the evolution has not b will be found deposited on the platinum foil as ent dark coating or stain. Therefore when test-tube is all or nearly all consumed, transfe of the tube to a porcelain dish and examine foil for this indication of the presence of antim

In the operation just performed, the tin wh oxide has been converted into the metallic s awaits examination in the porcelain dish. Re any zinc, remaining undissolved and carefully d dark spongy mass in the dish, the solution w

54

covered and which consists mainly of chloride of zinc. The residue is warmed with strong chlorhydric acid, in which the tin dissolves. Pour off the solution of stannous chloride

Test

for

Sn.

thus obtained, and add to it two or three drops of a solution of mercuric chloride (corrosive sublimate) (App., § 54). A white or gray precipitate of mer curous chloride (calomel), often mixed with gray metalli✔ mercury will be thrown down, for:

2HgCl,+SnCl,-Hg,Cl2+SnCl; and
Hg,Cl,+SnCl2=2Hg+SnCL .

To prove that the precipitate really contains calomel, decant the supernatant liquid, cover the precipitate with ammonia-water, and heat the mixture to boiling (compare p. 18). 26. An outline of the foregoing operations may be represented in tabular form as follows:

The General Reagent (H,S) of Class III precipitates As,S3, Sb2S3, and SnS or SnS,, [Au‚S, and [PtS2]. (As well as the members of Class II, from which Class III is separated by solution in sulphydrate of sodium.) The sulphydrate of sodium solution is treated with nitric acid and nitrate of sodium, and the mixture evaporated and heated to fusion. The fused mass is treated with cold water:

Arseniate of sodium

Antimoniate of sodium and oxide of tin (with nitrate of so- remain undissolved. Reduce with zinc dium, etc.) goes into and HCl in presence of platinum foil. solution. Confirm pres

silver test.

ence of As by magnesium mixture and by the Antimoniuretted hy- Tin is left in the drogen is formed and metallic state (toantimony spots ob-gether with some antained. timony which stains the foil). Dissolve the tin in HCl and test with HgCl,.

In the case of mixtures containing gold and platinum (see § 13), as well as arsenic, antimony and tin, the gold and platinum would remain with the tin, without interfering in any way with the separation or detection of either member of the

class, and when the tin reduced by zinc is disso hydric acid, the gold and platinum would rema (together with some antimony, if present). phides of gold and platinum are both black, arsenic and tin are yellow or brown, and that orange, the presence of any considerable qua of the precious metals would be indicated by t of the class precipitate.

There are excellent special tests both for gol inum, by which these elements may be detecte presence of all the other metals. Hence it is ient to make special search for them in the origi by methods to be described hereafter (§ 96, b.), preliminary examination has given reason to presence of either of them.

27. The method of separating Class II fr has been sufficiently described in §§ 8, 24. W of Class II are altogether absent, something m from the color of the precipitate produced by hydrogen. Thus, —

An orange colored precipitate indicates the antimony;

A bright yellow precipitate, the presence of a A dull yellow precipitate, white at first, th bisulphide of tin (stannic sulphide).

A dark brown precipitate, the presence of pro tin (stannous sulphide).

A black precipitate the presence of gold or p When, as a result of the preliminary exami III, c), there is reason to suspect the presen as a mercuric salt, sulphydrate of ammonium come somewhat yellow from standing, should 1 for sulphydrate of sodium, because sulphide rather soluble in sulphydrate of sodium. In th analysis of an unknown solution, if on the t nitric acid of the solution of sulphides in sulpl

dium, a black precipitate appear, it may be owing to the presence of sulphide of mercury and not to gold and platinum; it is therefore sometimes better in such a case to dilute the solution with water, filter and treat the precipitate with sulphydrate of ammonium. The precipitate remaining undissolved is added to the regularly obtained precipitate of Class II, and the sulphydrate of ammonium solution added, with a fresh portion of strong acid, to the nitric acid solution already obtained.

If an abundant supply of the substance under examination be at hand, it will often be better to start with a fresh portion and make the separation of the two classes with sulphydrate of ammonium.

Sulphide of copper is also somewhat soluble in the sulphydrates of sodium and ammonium, in presence of the sulphides of Class III; but enough of this sulphide will always remain undissolved to ensure the detection of copper in Class II.

Since sulphydrate of ammonium often fails to dissolve sulphide of tin, it is not, in general, so fit a solvent for the sulphides of Class III as sulphydrate of sodium. In either case it is desirable to use no more of the alkaline sulphydrate than is necessary, on account of the amount of sulphur which it will be necessary to oxidize with nitric acid and nitrate of sodium.

For another method of treading the sulphides of Class III, see page 127.

e pres m; it

- solu

-drate

ed is

, and

fresh y ob

ation rtion

Irate

phy

ides

main

sul

the

her

-ate

ich

of

II,

CHAPTER V.

CLASS IV. - ELEMENTS WHOSE HYDRATES ARE INSOL
BLE IN WATER, AMMONIA-WATER AND SOLUTION
OF AMMONIUM SALTS.

28. The leading fact upon which the separation of th class is based is the insolubility of the hydrates of iron, alum num and chromium in ammonia-water, even in presence solutions of ammonium salts. But these three hydrates a not the only substances which are liable to be precipitated an actual analysis when ammonia-water is added in excess a solution previously acid. There are a number of con pounds, soluble in acids, but not in water or in weak alkali liquids, which are thrown down without change when the acid solvent is destroyed.

It is clear that it is needless to provide in this place again the presence of such salts of elements belonging to Classes II and III. Those elements are already eliminated when t fourth class is taken in hand. But if there are any salts elements belonging to the fourth and higher classes which ca only be kept in solution by a free acid, they will be precip tated without change in consequence of the neutralization their solvent by the ammonia-water added to precipitate t three hydrates above mentioned. Such salts are the pho phates of several members of Classes IV, VI and VII, besid a number of oxalates, borates, silicates and fluorides whic occur so seldom that they need not be particularly considere in an elementary treatise. Beside the phosphates, several chr mites and aluminates of members of Classes VI and VII a insoluble in ammonia-water, and are often thrown down whol or in part along with the legitimate members of Class I

Manganese also (a member of Closs V) is frequently precir