Third class.-SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER AS WELL AS IN HYDROCHLORIC ACID, NITRIC ACID, AND AQUA REGIA.

The solution of alloys being more appropriately effected in a different manner from that pursued with other bodies, I shall give a special method for these substances (see § 181).

The process of solution is conducted in the following manner.

A. THE SUBSTANCE UNDER EXAMINATION IS NEITHER A
METAL NOR AN ALLOY.

$180.

1. Put about a gramme of the finely pulverized substance 32 into a small flask or a test-tube, add from ten to twelve times the amount of distilled water, and heat to boiling over a spirit or gaslamp.

a. THE SUBSTANCE DISSOLVES COMPLETELY. In that 33 case it belongs to the first class; regard must be had to what has been stated in the preliminary examination (30) with respect to reaction. Treat the solution either as directed § 182, or § 189, according as either one or several acids and bases are supposed to be present.

b. AN INSOLUBLE RESIDUE REMAINS EVEN AFTER PRO- 34 TRACTED BOILING. Let the residue subside, and filter the fluid off, if practicable in such a manner as to retain the residue in the test-tube; evaporate a few drops of the clear filtrate on platinum foil; if nothing remains, the substance is completely insoluble in water; in which case proceed as directed 35. But if a residue remains, the substance is at least partly soluble; in which case boil again with water, filter, add the filtrate to the first solution, and treat the fluid, according to circumstances, either as directed § 182, or § 189. Wash the residue with water, and proceed as directed 35.

2. Treat a small portion of the residue which has been boiled 35 with water (34) with dilute hydrochloric acid. If it does not dissolve, heat to boiling, and if this fails to effect complete solution, decant the fluid into another test-tube, boil the residue with concentrated hydrochloric acid, and, if it dissolves, add the solution to the fluid in the other test-tube.

The reactions which may manifest themselves in this operation, and which ought to be carefully observed, are, (a) Effervescence, which indicates the presence of carbonic acid or hydrosulphuric acid; (3) Evolution of chlorine, which indicates the presence of peroxides, chromates, &c.; (y) Emission of the odor of bydrocyanic acid, which indicates the presence of insoluble cyanides. The analysis of the latter bodies being effected in a somewhat different manner, a special paragraph will be devoted to them (see § 204).

a. THE RESIDUE IS COMPLETELY DISSOLVED BY THE 36 HYDROCHLORIC ACID (except perhaps that sulphur separates, which may be known by its color and light specific gravity, and may, after boiling some time longer, be removed by filtration; or that gelatinous hydrate of silicic acid separates).

Proceed, according as there is reason to suppose the presence of one or of several bases and acids, either as directed § 185, or as directed § 190 after filtration if necessary. The body belongs to the second class. To make quite sure of the actual nature of the sulphur or hydrated silicic acid filtered off, examine these residuary matters as directed § 188, or § 203.

b. THERE IS STILL A RESIDUE Left. In that case put 37 aside the test-tube containing the specimen which has been boiled with the hydrochloric acid, and try to dissolve another sample of the substance insoluble in water, or already extracted with water, by boiling with nitric acid, and subsequent addition of water. Evolution of nitric oxide, or nitrous acid, by the action of the nitric acid, shows that a process of oxidation is taking place.

a. The sample is completely dissolved, or leaves no other 38 residue but sulphur or gelatinous silicic acid; in this case also the body belongs to the second class. Use this solution to test further for bases, as directed § 185, or, as the case may be, § 189, III. (109), and for the rest proceed as in 36.

B. There is still a residue left. Pass on to 40.

39 3. If the residue insoluble in water will not entirely dissolve 40 in hydrochloric acid nor in nitric acid, try to effect complete solution of it by means of nitro-hydrochloric acid. To this end mix the contents of the tube treated with nitric acid with the contents of the tube treated with concentrated hydrochloric acid; heat the mixture to boiling, and should this fail to effect complete solution, decant the clear fluid off from the undissolved residue, boil the latter for some time with concentrated nitro-hydrochloric acid, and add the decanted solution in dilute aqua regia as well as the solution in dilute hydrochloric acid, decanted in 35. Heat the entire mixture once more to boiling, and observe whether complete solution has now been effected, or whether the action of the concentrated nitro-hydrochloric acid has still left a residue. In the latter case filter the solution-if necessary after addition of some water*-wash the residue with boiling water, and proceed with the filtrate, and the washings added to it, as directed § 185, or § 190. In the former case proceed with the clear solution in the same way.†

4. If boiling nitro-hydrochloric acid has left an undissolved 41 residue, wash it thoroughly with water, and then proceed as directed § 188, or as directed § 203, according as there is reason to suppose the presence of only one or several bases and acids.

*If the fluid turns turbid upon addition of water, this indicates the presence of bismuth or antimony; the turbidity will disappear again upon addition of hydrochloric acid.

+ Where the acid solution on cooling deposits acicular crystals, the latter generally consist of chloride of lead; it is in that case often advisable to decant the fluid off the crystals, and to examine the fluid and crystals separately. Where on boiling with aqua regia metastannic chloride has been formed from binoxide of tin, the washing water, dissolving this, becomes turbid on dropping into the strongly acid fluid which has run off first. In that case receive the washing water in a separate vessel, and treat the two solutions separately with hydrosulphuric acid as directed in § 190, but filter afterwards through the same filter.

B. THE SUBSTANCE UNDER EXAMINATION IS A METAL OR

AN ALLOY.

§ 181.

The metals are best classed according to their behavior with 42 nitric acid, as follows:

I. METALS WHICH ARE NOT ATTACKED BY NITRIC ACID : gold, platinum.

II. METALS WHICH ARE OXIDIZED BY NITRIC ACID, BUT

WHOSE OXIDES DO NOT DISSOLVE IN AN EXCESS OF THE ACID OR

IN WATER: antimony, tin.

III. METALS WHICH ARE OXIDIZED BY NITRIC ACID AND CON

VERTED INTO NITRATES WHICH DISSOLVE IN AN EXCESS OF THE

ACID OR IN WATER: all the other metals.

Pour nitric acid of 1.20 sp. gr. over a small portion of the substance, and apply heat.

I. COMPLETE SOLUTION TAKES PLACE, EITHER AT ONCE OR 43 UPON ADDITION OF WATER; this proves the absence of platinum,* gold, antimony,† and tin. Proceed either as directed § 182, or § 189, III. (109), according as there is reason to suppose the presence of only one or of several metals.

2. A RESIDUE IS LEFT.

a. A metallic residue. Filter, and treat the filtrate as directed 44 § 189, III. (109), after having seen, in the first place whether anything has really been dissolved. Wash the residue thoroughly, dissolve in nitro-hydrochloric acid, and test the solution for GOLD and PLATINUM, according to § 128.

b. A white pulverulent residue; indicates ANTIMONY and TIN. 45 Filter, ascertain whether anything has been dissolved, then treat the filtrate as directed § 189, III. (109). Wash the residue thoroughly, then test for TEROXIDE OF ANTIMONY, BINOXIDE OF TIN, and ARSENIC ACID, according to § 134, 5. (Part, at least, of the arsenic acid is always found in this precipitate, combined with teroxide of antimony and binoxide of tin.)

Alloys of silver and platinum, with the latter metal present in small proportion only, dissolve in nitric acid.

Very minute traces of antimony, however, are often completely dissolved by nitric acid.

236

III. ACTUAL EXAMINATION.

Simple Compounds.*

A. SUBSTANCES SOLUBLE IN WATER.

Detection of the Base.†

§ 182.

1. Add some hydrochloric acid to a portion of the aqueous 46 solution.

a. No PRECIPITATE IS FORMED; indicates the absence of silver and suboxide of mercury, and likewise the absence of considerable quantities of lead. Pass on to 50.

b. A PRECIPITATE IS FORMED. Divide the fluid in which 47 the precipitate is suspended into two portions, and add ammonia in excess to the one.

a. The precipitate redissolves, and the fluid becomes clear: this shows the precipitate to have consisted of chloride of silver. and is consequently indicative of the presence of SILVER. To arrive at a positive conviction on this point, the original solution must be tested with chromate of potassa, and with hydrosulphuric acid (see § 115, 4, and § 138, 7).

B. The precipitate turns black: this shows the precipitate 48 to have consisted of subchloride of mercury, which has now been converted by the ammonia into the black compound; it is consequently indicative of the presence of SUBOXIDE OF MERCURY. To set all doubt at rest, test the original solution with protochloride of tin, and with metallic copper (see § 116).

y. The precipitate remains unaltered: it consists of chloride 49 of lead, which is not dissolved by ammonia; this reaction is accordingly indicative of the presence of LEAD. Whether the precipitate consists really of chloride of lead or not is conclusively ascertained: 1st, by diluting the second portion of the fluid in which the precipitate produced by hydrochloric acid is suspended, with a large amount of water, and applying heat; the precipitate must dissolve if it consists of chloride of lead; and 2nd, by testing portions of the original solution with hydrosulphuric acid and sulphuric acid (§ 117, 4, and 8).

2. Add to the fluid acidified with hydrochloric acid solution of 50 hydrosulphuric acid until it smells distinctly of that gas after shaking, heat the mixture, add some more solution of hydrosulphuric acid, and let it stand a short time.

* This term is used to designate compounds supposed to contain only one base and one acid, or one metal and one non-metallic element. The principal object of this chapter is to facilitate instruction in analysis, as it is advantageous that the examination of complex com,ounds should be preceded by the analysis of simple compounds. In actual practical analyses, use can be made of this chapter only exceptionally, as there exists no outward sign by which to judge whether a substance contains only one base or acid, or several.

+ Arsenious and arsenic acids, and silicic acid are included here.

If a precipitate forms inmediately upon addition of solution of hydrosulphuric

a. THE FLUID REMAINS CLEAR. Pass on to 56, since this is a proof that lead, bismuth, copper, cadmium, oxide of mercury, gold, platinum, tin, antimony, arsenic, and sesquioxide of iron are not present.

b. A PRECIPITATE IS FORMED.

a. THE PRECIPITATE IS WHITE; it consists of separated 51 sulphur, and indicates a substance which decomposes hydrosulphuric acid.* Of the metallic oxides which possess this property SESQUIOXIDE OF IRON is the most common (§ 111, 3). Test for this with ammonia and ferrocyanide of potassium in the original solution (§ 111, 5 and 6). If it is not found pass on to 56.

B. THE PRECIPITATE IS YELLOW; it may consist of 52 sulphide of cadmium, sulphide of arsenic, or bisulphide of tin, it indicates accordingly cadmium, arsenic, or binoxide of tin. To distinguish between them, mix a portion of the fluid wherein the precipitate is suspended with ammonia in excess, add some sulphide of ammonium, and warm.

aa. The precipitate does not dissolve: it consists of CADMIUM; for sulphide of cadmium is insoluble in ammonia and sulphide of ammonium. Confirm by testing the original substance, or the precipitate thrown down from the original solution by carbonate of ammonia, with the blowpipe (§ 122, 9).

bb. The precipitate dissolves: BINOXIDE OF TIN or ARSENIC: add ammonia to a small portion of the original solution.

Y.

aa. A white precipitate is formed. BINOXIDE OF TIN is the substance present. Confirm by reducing the precipitate before the blowpipe, with cyanide of potassium and carbonate of soda (5 130, 8).

BB. No precipitate is formed. This indicates ARSENIC. Confirm by the production of an arsenical mirror from the original substance or the precipitated sulphide of arsenic, either with cyanide of potassium and carbonate of soda, or in some other way; and moreover by exposing the original substance with carbonate of soda to the inner flame of the blowpipe (§ 132, 12 and 13). If the solution contained arsenious acid, the yellow precipitate formed immediately upon the addition of the hydrosulphuric acid; if arsenic acid, it formed only upon the application of heat, or after long standing. For further information respecting the means of distinguishing between the two acids see § 134, 9.

THE

PRECIPITATE IS ORANGE-COLORED, it consists 53 of tersulphide of antimony, and indicates TEROXIDE OF ANTIMONY. For confirmation the original solution is tested with zinc in a platinum capsule (§ 131, 8).

8. THE PRECIPITATE IS DARK-BROWN. It consists of 54 protosulphide of tin, and indicates PROTOXIDE of tin. To

acid, it is unnecessary to apply heat, &c.; but if the fluid remains clear, or is rendered only slightly turbid, the above course of proceeding must be strictly followed, to guard against the risk of overlooking arsenic acid and binoxide of tin.

* If the color of the solution from being reddish yellow changes to green, chromic acid is indicated.