YELLOWISH-BROWN, on cooling changing to light yellow or BRIGHT YELLOWISH to OPAL, when cold rather dull; in the AMETHYST-RED, especially on cooling; colorless in the re- 6. The hot bead is colorless: IT REMAINS CLEAR ON COOLING: ANTIMONY, ALUMINA, ZINC, IT BECOMES ENAMEL-WHITE ON COOLING, even when only 19 b. THE SUBSTANCE DISSOLVES SLOWLY AND ONLY IN SMALL 20 QUANTITY: a. The bead is colorless, and remains so even after cooling; the undissolved portion looks semi-transparent; upon addition of a little sesquioxide of iron, it acquires the characteristic color of an iron bead: SILICIC ACID. 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 THE 21 METALLIC STATE) IN THE BEAD: GOLD, PLATINUM. As the body under examination may consist of a mixture of the most dissimilar elements, it is impossible to give well defined cases that shall offer at the same time the advantage of general applicability. If, therefore, reactions are observed in an experiment which proceed from a combination of two or several cases, the conclusions drawn from these reactions must of course be modified accordingly. § 175. II. THE SUBSTANCE IS A METAL OR AN ALLOY. 1. Heat a small portion of the substance with water acidulated 22 with acetic acid. a. HYDROGEN GAS IS EVOLVED: this indicates the presence of a light metal (possibly also of manganese in the metallic state). The presence of alkalies and of alkaline earths must also be had regard to in the actual examination. b. No HYDROGEN IS EVOLVED: this indicates the absence of light metals. Alkalies and alkaline earths may be altogether disregarded in the course of the special investigation. 2. Heat a sample of the substance on charcoal in the reducing 23 flame of the blowpipe, and watch the reactions; for instance, whether the substance fuses, whether an incrustation is formed, or an odor emitted, &c. a. THE SAMPLE REMAINS UNALTERED: this is pretty conclusive of the absence of antimony, zinc, lead, bismutn, cadmium, tin, mercury, and arsenic; the absence of gold, silver, and copper is also probable; PLATINUM, IRON, MANGANESE, NICKEL, and COBALT are likely to be present. b. THE SAMPLE FUSES; NO INCRUSTATION FORMS, AND NO ODOR IS EMITTED: absence of antimony, zinc, lead, bismuth, cadmium, and arsenic; presence of GOLD, SILVER, COPPER. C. THE SAMPLE FUSES, AND AN INCRUSTATION IS FORMED, BUT NO ODOR EMITTED: absence of arsenic, and presence of ANTIMONY, ZINC, BISMUTH, LEAD, CADMIUM (compare § 174, 3, c, ß [16]). d. THE SUBSTANCE EMITS THE ODOR OF GARLIC; ARSENIC is present. According to the nature of the other reactions which may manifest themselves, a, b, or c must be had regard to. 3. Heat a sample of the substance before the blowpipe in a glass 24 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 possibly be confounded with that of cadmium or arsenic. $ 176. B. THE SUBSTANCE UNDER EXAMINATION IS A FLUID. 1. Evaporate a small portion of the fluid in a platinum dish, or in 25 a small porcelain crucible, to ascertain whether it actually contains any matter in solution; if a residue remains, examine this as directed $174. 2. Test with litmus paper (blue and red). a. THE FLUID REDDENS BLUE LITMUS PAPER. This reaction may be caused by a free acid or an acid salt, as well as by a metallic salt soluble in water. To distinguish between these two cases, pour a small quantity of the fluid into a watch-glass, and dip into it a small glass rod, the extreme point of which has previously been moistened 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. As a matter of course, a solution which contains a free acid or an acid salt can no longer be considered simply aqueous, and the subsequent examination must accordingly be conducted with due regard to the possible presence of substances insoluble in water but soluble in acids. 26 6. REDDENED LITMUS PAPER TURNS BLUE: this indicates the 27 presence of free alkalies or alkaline carbonates, free alkaline earths, alkaline sulphides, and of a number of other salts which show this reaction. In presence of a free alkali, a body dissolved in a fluid is as likely to belong to the class of substances soluble, as to that of bodies insoluble in water. For the way to settle this point, and also for further information on 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; (6) 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 § 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.t 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 platinum. NOT ATTACKED BY NITRIC ACID: gold, 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 acid. acid. Very minute traces of antimony, however, are often completely dissolved by nitric |