the way to settle this point, and also for further information on the subject of alkaline solutions in general, I refer to § 187, I. 2 (104). 3. Smell the fluid or, should this fail to give satisfactory results, 28 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 § 174. 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 and turbid appearance to it, the presence of ANTIMONY, BISMUTH (possibly also of tin) may be inferred. If the precipitate disappears upon the addition of tartaric acid, there is reason to believe it consists of antimony; if it is not redissolved by tartaric acid, but by nitric acid, you may assume the presence of bismuth. Treat the original fluid either as directed § 180 or as directed § 187, according as you have reason to suppose it to be the solution of a simple or a compound (mixed) substance. II. SOLUTION OF BODIES, OR CLASSIFICATION OF SUBSTANCES ACCORDING ΤΟ THEIR DEPORTMENT WITH CERTAIN SOLVENTS.* $177. Water, hydrochloric or nitric acid, and aqua regia are the solvents 30 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 respective behavior 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. Third class.-SUBSTANCES INSOLUBLE OR DIFFICULTLY 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 § 179). The process of solution is conducted in the following manner. A. THE SUBSTANCE UNDER EXAMINATION IS NEITHER A METAL NOR AN ALLOY. § 178. 1. Put about a gramme (15·5 grains) of the finely pulverized sub- 31 stance under examination 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 gas-lamp. a. THE SUBSTANCE DISSOLVES COMPLETELY. In that case it 32 belongs to the first class; regard must be had to what has been * Consult the remarks in the third section. stated in § 176, 2 (26), concerning the reactions with testpapers. Treat the solution either as directed § 180 or as directed § 187, according as either one or several acids and bases are supposed to be present. b. AN INSOLUBLE RESIDUE REMAINS, EVEN AFTER PROTRACTED 33 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 § 178, 2 (34). 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 original solution, and treat the fluid, according to circumstances, either as directed § 180, or according to § 187. Wash the residue with water, and proceed as directed $ 178, 2 (34). 2. Treat a small portion of the residue which has been boiled with 34 water (33) 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 it 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 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 § 202). a. THE RESIDUE IS COMPLETELY DISSOLVED BY THE HYDRO- 35 CHLORIC 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 to circumstances, either as directed § 183, or as directed § 188, after previous 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 § 186, or as directed § 201. b. THERE IS STILL A RESIDUE LEFT. In that case put aside 36 the test-tube containing the specimen which has been boiled with the hydrochloric acid, and try to dissolve another sample of the substance under examination, by boiling with nitric acid, and subsequent addition of water. a. The sample is completely dissolved, or leaves no other 37 residue but sulphur or the gelatinous hydrate of silicic acid; in this case also the body belongs to the second class. Use this solution to test further for bases, and then proceed as directed in 2, a (35). B. After boiling with nitric acid there is still a residue left. 38 Pass on to 3. 3. If the residue insoluble in water will not entirely dis- 39 solve in hydrochloric acid nor n 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 nitrohydrochloric acid, and add the decanted solution in dilute aqua regia as well as the solution in dilute hydrochloric acid decanted in § 178, 2 (34). 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 § 183, or as directed § 188;-in the former case, proceed with the clear solution in the same way.† 4. If boiling nitrohydrochloric acid has left an undissolved re- 40 sidue, wash it thoroughly with water, and then proceed as directed § 186, or as directed § 201. B. THE SUBSTANCE UNDER EXAMINATION IS A METAL OR AN ALLOY. The metals are best classed according to their respective behavior 41 with nitric acid: this gives us, I. METALS WHICH ARE NOT ATTACKED BY NITRIC ACID : gold, platinum. II. METALS WHICH ARE OXIDIZED BY NITRIC ACID, BUT OF WHICH THE OXIDES DO NOT DISSOLVE IN AN EXCESS OF THE ACID NOR 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 other metals. Pour nitric acid of 1.25 sp. gr. over a small portion of the metal or alloy under examination, and apply heat. 1. COMPLETE SOLUTION TAKES PLACE, EITHER AT ONCE OR UPON 42 ADDITION OF WATER; this proves the absence of platinum,‡ gold, antimony, and tin. Proceed, according to circumstances, either as directed § 183, or as instructed § 187, III. (109). 2. A RESIDUE IS LEFT. a. A metallic residue. Filter, and treat the filtrate as di- 43 rected § 187, III., after having examined, in the first place, *If the fluid turns turbid upon addition of water, this indicates the presence of bismuth or antimony; the turbidity disappears again upon addition of hydrochloric acid. If 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 from the crystals, and to examine fluid and crystals separately. Alloys of silver and platinum, with the latter metal present in small proportion only, dissolve in nitric aoid. Very minute traces of antimony, however, are often completely dissolved by nitric whether anything has really been dissolved. Wash the residue b. A white, pulverulent residue; this indicates the presence 44 of ANTIMONY and TIN. Filter, ascertain whether anything has been dissolved, and if so treat the filtrate as directed § 187, III. Wash the residue thoroughly, and heat it with a hot saturated solution of bitartrate of potassa, or with a solution of tartaric acid. a. Complete solution ensues; this indicates the presence of 45 oxide of ANTIMONY alone; test the solution with hydrosulphuric acid, after addition of some hydrochloric acid. B. A white residue remains, even after boiling with a fresh portion of solution of bitartrate of potassa or tartaric acid; this indicates the probable presence of TIN. Filter and mix the filtrate with some hydrochloric acid, then with solution of hydrosulphuric acid. If an orange-red precipitate is formed, TEROXIDE OF ANTIMONY is present. It is always necessary to ascertain whether the residue consists really of binoxide of tin: which may be known by heating it to redness, then fusing it in a small tube with cyanide of potassium, boiling the reduced metal with water, then heating with hydrochloric acid, and testing the solution with chloride of mercury (§ 133). III. ACTUAL EXAMINATION. Simple Compounds.* A. SUBSTANCES SOLUBLE IN WATER. Detection of the Base.+ $ 180. 1. Add some hydrochloric acid to a portion of the aqueous solu- 46 tion. a. NO PRECIPITATE IS FORMED; this is a positive proof of the absence of silver and suboxide of mercury, and is likewise an indication of the probable absence of lead. Pass on to § 180, 2 (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. * This term is used here, and wherever it happens to occur hereafter in the present work, to designate compounds supposed to contain only one base and one acid, or one metal and one non-metallic element. Arsenious acid and arsenic acid are included here. To arrive at a positive conviction on this point, the original solution must be tested with chromate of potassa, and with hydrosulphuric acid (see § 114, 4, and § 138, b, 6). 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 suboxide of mercury; it is consequently indicative of, the presence of SUBOXIDE OF MERCURY. To set all doubt on this point at rest, test the original solution with protochloride of tin, and with metallic copper (see § 115). 7. The precipitate remains unaltered; it consists in that 49 case of chloride 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 cousists of chloride of lead; and 2nd, by adding dilute sulphuric acid to the original solution (§ 116, 8). 2. Add to the fluid acidified with hydrochloric acid (1) solution 50 of hydrosulphuric acid until it smells distinctly of that gas, even after shaking, and heat the mixture. a. THE FLUID REMAINS CLEAR. Pass on to 3 (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. THIS PRECIPITATE IS WHITE; it consists in that case of 51 separated sulphur, and is indicative of the presence of SESQUIOXIDE OF IRON (§ 110, 3). However, as the separation of sulphur may also be caused by other substances, it is indispensable that you should satisfy yourself whether the substance present is really sesquioxide of iron or not. For this purpose test the original solution with ammonia, and with ferrocyanide of potassium (§ 110, 5 and 6). B. THE PRECIPITATE IS YELLOW; in that case it may con- 52 sist either of sulphide of cadmium, sulphide of arsenic, or bisulphide of tin; it indicates accordingly the presence of either 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 heat. aa. The precipitate does not dissolve; it consists of CADMIUM; for sulphide of cadmium is insoluble in ammonia and sulphide of ammonium. The blowpipe is resorted to as a confirmatory test (§ 121, 8). bb. The precipitate dissolves: BINOXIDE OF TIN or ARSENIC; add ammonia to a small portion of the original solution. aa. A white precipitate is formed. BINOXIDE OF TIN is the substance present. Positive conviction is obtained by reducing the precipitate before the blowpipe, |