Test the reaction of the condensed fluid in the tube: if it is alkaline, ammonia may be assumed to be present; if acid, a volatile acid (sulphuric acid, sulphurous acid, hydrofluoric acid, hydrochloric, hydrobromie, or hydriodic acids, nitric acid, &c.). e. GASES OR FUMES ESCAPE. Observe whether they have a 8 color, smell, acid or alkaline reaction, whether they are inflammable, &c. aa. OXYGEN. The disengagement of this gas indicates the presence of peroxides, chlorates, nitrates, &c. A glimmering slip of wood is relighted in the gaseous current. bb. SULPHUROUS ACID. This is often produced by the decomposition of sulphates; it may be known by its peculiar odor and by its acid reaction. cc. HYPONITRIC ACID, resulting from the decomposition of nitrates, especially with oxides of the heavy metals; it may be known by the brownish-red color of the fumes. dd. CARBONIC ACID. The evolution of carbonic acid indicates the presence of carbonates decomposable by heat. The gas evolved is colorless and tasteless, non-inflammable; a drop of lime-water on a watch-glass becomes turbid on exposure to the gaseous current. ee. CARBONIC OXIDE GAS. The escape of this gas indicates the presence of oxalates, and, when attended with actual carbonization, also of formates. The gas burns with a blue flame. ff. CYANOGEN. The evolution of cyanogen gas denotes the presence of cyanides decomposable by heat. The gas may be known by its odor, and the crimson flame with which it burns. gg. HYDROSULPHURIC ACID GAS. The escape of hydrosulphuric acid gas indicates the presence of sulphides containing water; the gas may be readily known by its odor. hh. AMMONIA, resulting from the decomposition of ammoniacal salts, or also of cyanides or nitrogenous organic matters, in which latter cases browning or carbonization of the substance takes place, and either cyanogen or offensive empyreumatic oils escape with the ammonia. f. A SUBLIMATE FORMS. This indicates the presence of vola- 9 tile bodies: the following are those more frequently met with : aa. SULPHUR. Separated from mixtures or from many of the metallic sulphides. Sublimes in reddish-brown drops which become solid on cooling, and turn yellow, or yellowishbrown. bb. AMMONIA SALTS give white sublimates; heated with soda and a drop of water on platinum foil, they evolve ammonia. cc. MERCURY and compounds of mercury. METALLIC MERCURY forms globules; SULPHIDE OF MERCURY is black, but acquires a red tint when rubbed; CHLORIDE OF MERCURY fuses before volatilizing; SUBCHLORIDE OF MERCURY sublimes without previous fusion; the sublimate, which is yellow whilst hot, turns white on cooling. The red IODIDE OF MERCURY gives a yellow sublimate. dd. ARSENIC and compounds of that metal. METALLIC ARSENIC forms the well-known arsenical mirror; ARSENIOUS ACID forms small shining crystals; the SULPHIDES OF ARSENIC give sublimates which are reddish-yellow whilst hot, and turn yellow on cooling. ee. TEROXIDE OF ANTIMONY fuses to a yellow liquid before subliming. The sublimate consists of brilliant needles. ff. BENZOIC ACID and SUCCINIC ACID, which may be known by the odor of their fumes. gg. HYDRATED OXALIC ACID. White crystalline sublimate, thick fumes in the tube. Heating a small sample on platinum foil with a drop of concentrated sulphuric acid gives rise to a copious evolution of gas. This 10 g. CARBONIZATION TAKES PLACE organic substances. is always attended with evolution of gases (in the case of acetates of acetone) and water, which latter has an alkaline or acid reaction. If the residue effervesces with acids, whilst the original substance did not show this reaction, organic acids may be assumed to be present in combination with alkalies or alkaline earths. 3. Put a small portion of the substance on a charcoal support (in 11 the cavity scooped out for the purpose), and expose to the inner blowpipe flame. As most of the reactions described under 2 (3-10) are also produced by this process, I will here enumerate only those which result more particularly and exclusively from its application. a. THE BODY FUSES, AND IS ABSORBED BY THE CHARCOAL OR 12 FORMS A BEAD IN THE CAVITY: this denotes more particularly the presence of salts of the alkalies. 6. AN INFUSIBLE WHITE RESIDUE REMAINS on the charcoal, 13 either at once or after previous melting in the water of crystallization. This indicates more particularly the presence of baryta, strontia, lime, magnesia, alumina, oxide of zinc (which appears yellow whilst hot), and silicic acid. Among these substances, STRONTIA, LIME, MAGNESIA, and OXIDE OF ZINC, are distinguished by strong luminosity in the blowpipe flame. Moisten the white residue with a drop of solution of nitrate of protoxide of cobalt, and expose again to a strong heat. If the mass assumes a fine blue tint, this indicates the presence of ALUMINA; if a reddish tint, of MAGNESIA; if a green color, of OXIDE OF ZINC. If SILICIC ACID is present, the mass also assumes a faint bluish tint, which must not be confounded with that proceeding from the presence of alumina. C. THE SUBSTANCE LEAVES AN INFUSIBLE RESIDUE OF 14 ANOTHER COLOR, OR REDUCTION ΤΟ THE METALLIC STATE TAKES PLACE, WITH OR WITHOUT INCRUSTATION OF THE CHARCOAL. Mix a portion of the powder with carbonate of soda, and heat on charcoal in the reducing flame; observe the residue in the cavity, as well as the incrustation on the charcoal. a. The sustained application of a strong flame produces a me- 15 tallic globule, without incrustation of the charcoal; this indi cates the presence of GOLD, SILVER, or COPPER. The oxides of platinum, iron, cobalt, and nickel, are indeed also reduced, but they yield no metallic globules. B. The charcoal support is coated with an incrustation, 16 either with or without simultaneous formation of a metallic globule. aa. The incrustation is white, at a long distance from the test specimen, and is very readily dissipated by heat, emitting a garlic-like odor: ARSENIC. bb. The incrustation is white, is nearer the test specimen than in aa, and may be driven from one part of the support to another: ANTIMONY. Metallic globules are generally observed at the same time, which continue to evolve white fumes long after the blowpipe jet is discontinued, and upon cooling become surrounded with crystals of teroxide of antimony; the globules are brittle. cc. The incrustation is yellow whilst hot, but turns white on cooling; it is near the test specimen, and is with difficulty volatilized: ZINC. dd. The incrustation has a faint yellow tint whilst hot, but turns white on cooling; it surrounds the test specimen, and both the inner and outer flame fail to volatilize it: TIN. The metallic globules formed at the same time are bright, readily fusible, and malleable. ee. The incrustation has a lemon-yellow color, turning on cooling to sulphur-yellow; when exposed to the reducing flame, it leaves a bluish stain: LEAD. Readily fusible, malleable globules are formed at the same time with the incrustation. The incrustation is of a dark orange-yellow color whilst hot, which changes to lemon-yellow on cooling; when exposed to the reducing flame, it does not leave a bluish stain: BISMUTH. The metallic globules formed at the same time as the incrustation are readily fusible and brittle. gg. The incrustation is reddish-brown, in thin layers, orange-yellow; it volatilizes without leaving a colored stain CADMIUM. 4. Fuse a small portion together with a bead of microcosmic salt, 17 and expose for some time to the outer flame of the blowpipe. a. THE SUBSTANCE DISSOLVES READILY AND RATHER LARGELY TO A CLEAR BEAD (WHILST HOT). a. The hot bead is colored: BLUE, by candlelight inclining to violet-COBALT ; GREEN, particularly fine on cooling, unaltered in the re- BROWNISH-RED, on cooling light yellow or colorless; in the reducing flame red whilst hot, yellow whilst cooling, then greenish-IRON; DARK YELLOW to REDDISH, turning lighter or altogether colorless on cooling; in the reducing flame unaltered— NICKEL ; 18 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- B. 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. 6. 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. 6. 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 2 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 |