B. The bead is colorless, and remains so after addition of a little sesquioxide of iron: TIN.

c. THE SUBSTANCE DOES NOT DISSOLVE, BUT FLOATS (IN 21 THE METALLIC STATE) IN THE BEAD: GOLD, PLATINUM.

5. MINERALS ARE EXAMINED FOR FLUORINE AS DIRECTED

§ 146, 8.

After the termination of the preliminary examination, proceed to the solution of the substance, as directed § 180 (32).

§ 177.

II. THE SUBSTANCE IS A METAL OR AN ALLOY.

1. HEAT A SMALL PORTION OF THE SUBSTANCE WITH 22 WATER ACIDULATED WITH ACETIC ACID. If HYDROGEN is evolved this indicates a light metal (possibly also manganese).

2. HEAT A SAMPLE OF THE SUBSTANCE ON CHARCOAL IN 23 THE REDUCING FLAME OF THE BLOWPIPE, and watch the reactions; for instance, whether the substance fuses, whether an incrustation is formed, or an odor emitted, &c.

By this operation the following metals may be detected with more or less certainty: ARSENIC by the smell of garlic; MERCURY by its volatility; ANTIMONY, ZINC, LEAD, BISMUTH, CADMIUM, TIN, SILVER, by fusing, with incrustation of the charcoal (comp. 16); COPPER by the green coloration of the outer flame. Further conclusions may be formed when the substance is a single metal nearly pure; thus, for instance GOLD fuses without incrustation; PLATINUM, IRON, MANGANESE, NICKEL, and COBALT, do not fuse in the blowpipe flame.

3. HEAT A SAMPLE OF THE SUBSTANCE BEFORE THE BLOW- 24

PIPE IN A GLASS TUBE SEALED AT ONE END,

a. No SUBLIMATE IS FORMED IN THE COLDER PART OF THE TUBE: absence of mercury.

b. A SUBLIMATE IS FORMED: presence of MERCURY, CADMIUM, or ARSENIC. The sublimate of mercury, which consists of small globules, cannot be confounded with that of cadmium or arsenic.

After the termination of the preliminary examination, proceed to the solution of the substance as directed § 181 (42).

§ 178.

B. THE SUBSTANCE UNDER EXAMINATION IS A FLUID. 1. EVAPORATE A SMALL PORTION OF THE FLUID in a pla- 25 tinum capsule, or in a small porcelain crucible, to ascertain whether it actually contains any matter in solution; if a residue remains, examine this as directed § 176.

2. TEST WITH LITMUS-PAPER (blue and red).

This re

a. THE FLUID REDDENS BLUE LITMUS-PAPER. action may be caused by a free acid or an acid salt, as well as by a metallic salt soluble in water. To distinguish between

26

these two cases, pour a small quantity of the fluid into a watchglass, and dip into it a small glass rod, after moistening the extreme point of the latter with dilute solution of carbonate of soda; if the fluid remains clear, or if the precipitate which may form at first, redissolves upon stirring the liquid, this proves the presence of a free acid or of an acid salt; but if the fluid becomes turbid and remains so, this generally denotes the presence of a soluble metallic salt.

b. REDDENED LITMUS-PAPER TURNS BLUE: this indicates 27 the presence of a free alkali or an alkaline carbonate, free alkaline earths, alkaline sulphides, and of a number of other salts containing an alkali or, it may be, an alkaline earth, in combination with a weak acid.

3. SMELL THE FLUID, or, should this fail to give satisfactory 28 results, DISTIL, to ascertain whether the simple solvent present is water, alcohol, ether, &c. If you find it is not water, evaporate the solution to dryness, and treat the residue as directed § 176.

4. If the solution is aqueous, and manifests an acid reaction, 29 DILUTE A PORTION OF IT LARGELY WITH WATER. Should this impart a milky appearance to it, the presence of ANTIMONY, or BISMUTH (or possibly also of tin) may be inferred. Comp. § 121, 9, and § 131, 4.

After the termination of the preliminary examination, proceed 30 to the actual examination. If the solution is aqueous, with neutral reaction, it can only contain substances soluble in water; but if it has an acid reaction, arising from the presence of free acid, the actual examination must be conducted with due regard to the possible presence also of bodies soluble in acids, though insoluble in water. Proceed accordingly with neutral aqueous solutions as directed § 182, with acid solutions as directed § 185, if you are quite sure that there is only one acid and one base present; but where there is reason to suppose the presence of several bases and acids, proceed as directed § 189. With fluids of alkaline reaction, proceed as directed § 182, unless there be reason to suppose the presence of more than one acid and one base, when the instructions given in § 189 must be followed.

II. SOLUTION OF BODIES, OR CLASSIFICATION OF SUBSTANCES, ACCORDING TO THEIR DEPORTMENT WITH CERTAIN SOLVENTS.*

§ 179.

Water and acids (hydrochloric acid, nitric acid, aqua regia) are 31 the solvents used to classify simple or compound substances, and to isolate the component parts of mixtures. We divide the various substances into three classes, according to their their respective deportment with these solvents.

First class.-SUBSTANCES SOLUBLE IN WATER.

Second class. - SUBSTANCES INSOLUBLE OR SPARINGLY SOLUBLE IN WATER, BUT SOLUBLE IN HYDROCHLORIC ACID, NITRIC ACID, OR AQUA REGIA.

*Consult the remarks in the third section.

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.; (7) Emission of the odor of hydrocyanic 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 behaviour 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 CONVERTED 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.

1. 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.