Ammonia.

§ 48. Small quantities of ammonia are best detected by mixing the powdered assay [No. 19] with some carbonate of soda or caustic potassa, introducing the mixture into a glass tube, sealed at one end, and applying heat. The escaping gas is characterized by its odor, and by its action on reddened litmus paper. From the appearance of this reaction we are, however, not authorized to infer the preexistence of ammonia in the assay, since from organic matter containing nitrogen, when subjected to this treatment, ammonia is evolved as a product of decomposition.

Antimony.

The reactions of antimony and its compounds, see § 11, § 16, § 21, § 36, and Table II, 1.

§ 49. In presence of lead or bismuth, antimony can not be detected by its Ct on Ch. In this case the metallic compound [No. 48, or No. 85] is treated with vitrified boracic acid on Ch, the flame being so directed that the glass is always kept covered with the blue cone, the metallic globule being on the side; by this means the metals become oxidized, the oxides of lead and bismuth are absorbed by the boracic acid, and the antimonious acid will form a ring on the Ch, provided the temperature was not raised too high. § 50. When combined with metals from which it is not easily separated, ex. gr. copper, the evaporation of the antimony takes place so slowly that no distinct Ct is produced. In this case the assay [No. 86] is treated with S Ph on Ch in the O Fl, until the antimony, or at least part of it, has become oxidized and entered into the flux. The glass is now removed from the metallic globule and treated on another place of the Ch with metallic tin in the R Fl; the presence of antimony will cause the glass to turn gray or black on cooling [Table II, 1]. Bismuth behaving under these circumstances in the same manner, the presence of this metal makes the reaction not decisive for antimony. The humid way

has then to be resorted to.

51. When the oxides of antimony are accompanied by such metallic oxides which, when reduced on Ch, fuse with the metallic antimony to an alloy, as is ex. gr. the case with the oxides of tin

and copper, the latter cannot be recognized by a simple reduction. The oxides have to be treated with a mixture of Sd and Bx on Ch in the R Fl. The little metallic globules are separated from the flux, and fused with from three to five times their own volume of pure lead and some vitrified boracic acid in the R Fl, care being taken to play with the flame only on the glass. Antimonious acid is volatilized, depositing the characteristic ring, while the oxides of the other metals are absorbed by the boracic acid.

§ 52. The sulphides of antimony, when heated in the open glass tube, show the reaction mentioned § 16. When accompanied by sulphide of lead [No. 89], only a small part of the antimony is converted into antimonious acid, which sublimes; the remainder is changed into a white powder consisting of a mixture of antimonate of oxide of antimony, sulphate of lead, and antimonate of lead. When a compound containing sulphide of lead or bismuth, besides sulphide of antimony, is heated on Ch in the R Fl, a Ct is deposited consisting of antimonious acid mixed with sulphate of lead or bismuth, and, nearer to the assay, a yellow one of the oxides of lead or bismuth; how in such a case the presence of antimony may be ascertained v. § 87.

§ 53. To detect a small amount of sulphide of a timony in sulphide of arsenic, Plattner strongly recommends the following method, by which he obtained very decisive and satisfactory results: The assay [No. 88] is introduced into a glass tube, sealed at one end, and gently heated; the sulphide of arsenic is volatilized, and the greater part of the sulphide of antimony remains as a black powder in the lower end of the tube; this end is cut off, the black substance taken out and transferred to a tube open at both ends. By applying heat the characteristic antimony-reaction will appear.

Arsenic.

The reactions of arsenic and its compounds, see § 11, § 15, § 20, § 34, and Table II, 2.

§ 54. All metallic arsenides yield, when heated in the open glass tube, a sublimate of arsenous acid (v. § 15), and most of them evolve a garlic odor (v. § 20) when heated on Ch in R Fl [No. 77].

Some metals, ex. gr. nickel and cobalt, have a great affinity for arsenic, so that, when only a small quantity of the latter is present, the characteristic odor is not observable; in such cases it is sometimes produced when the metallic compound is fused on Ch with some pure lead in the O Fl.

§ 55. The sulphides of arsenic, heated in the open glass tube, evolve sulphurous acid and yield a sublimate of arsenous acid. To show in a very decisive manner the presence of arsenic in any of its combinations with sulphur, the powdered assay [No. 80] is mixed with six parts of a mixture of equal parts of cyanide of potassium and carbonate of soda, the mass introduced into a tube sealed at one end, and heat applied, at first very gently but gradually raised to redness. A ring of metallic arsenic will be deposited in the colder part of the tube

§ 56. When sulph-arsenides are heated on Ch, the whole of the arsenic, especially when only small quantities are present, may pass off in combination with sulphur; but when such compounds [No. 88] are mixed with from three to four parts of cyanide of potassium and exposed to the R Fl, sulphide of potassium is formed and the arsenic escapes with its peculiar odor.

§ 57. To detect a very small quantity of arsenous acid, the following way may be pursued: a glass tube provided with a small. bulb at one end is close above it narrowly drawn out; the assay [No. 38] is introduced into the bulb, and a charcoal splinter placed into the tube; the narrow aperture through which the tube communicates with the bulb prevents the Ch from coming in contact with the substance. The tube is then heated to redness at the place where the charcoal splinter lies, and as soon as this is incandescent, heat is also applied to the bulb. The arsenous acid is volatilized, and its vapors, while passing over the red-hot charcoal, become reduced and deposit a black metallic ring of arsenic in the colder part of the tube. By cutting the tube below the ring and heating this part by the flame of a spirit-lamp, the arsenic is volatilized, thereby emitting its characteristic odor.

§ 58. To show the presence of arsenic in arsenites and arsenates, it will in most cases be sufficient to mix the substance [No. 38] with carbonate of soda and heat it on Ch in R Fl. Sometimes it

is necessary to treat the assay with a mixture of carbonate of soda and cyanide of potassium in the manner mentioned, § 55; and in other cases again, where but small quantities of arsenous or arsenic acid are combined with metallic oxides which are readily reduced, recourse must be had to the humid way.

Bismuth.

The reactions of bismuth and its compounds, see § 12, § 17, § 22, and Table II,

3.

§ 59. Bismuth when alloyed with other metals, or when as sulphide in combination with other sulphides, is in many cases, and most especially so when accompanied by lead or antimony, not to be detected by the ring which it deposits on Ch. In such a case the assay [No. 49] is treated on Ch until a copious yellow Ct is formed. The Ct is carefully scraped off from the Ch and dissolved in S Ph on platinum wire with the O Fl. The colorless bead is removed from the wire, placed on Ch, a little metallic tin added, and the whole exposed to the R Fl. If bismuth was present, the glass assumes, on cooling, a dark-gray or black color. The oxides of antimony showing the same behavior, the assay, if not quite free from antimony, has to be treated on Ch in the O Fl until the whole of it has been volatilized, and the remaining mass treated on another piece of Ch as above mentioned.

Boracic Acid.

§ 60. With many borates, which do not impart to the outer flame the peculiar yellowish-green color [v. § 35], this reaction may be produced by reducing the substance [No. 2] to powder, adding a drop of concentrated sulphuric acid, fastening the mixture into the hook of the platinum wire, and playing on it with the blue cone of the flame.

§ 61. Another way, and by which even a very small quantity of boracic acid in salts and minerals may be detected, is: to reduce the substance to a very fine powder, to mix it with from 3 to 4 parts of a mixture of 42 parts of bisulphate of potassa and 1 part of fluorspar, and to knead the whole with a little water into a thick paste. This mass is then fastened to a platinum wire, and exposed to the blue cone of the flame. While the mass enters into fusion fluoboric

acid is formed which, on escaping, colors the flame intensely yellowish-green. The reaction appearing sometimes only for a few seconds, the flame should be very attentively watched during the whole time of the experiment.

Bromine.

§ 62. Bromides treated with S Ph and oxide of copper on platinum wire, or treated with sulphate of copper on silver foil, show the same reaction as chlorides (v. § 66), with this difference, that the blue color of the outer flame is rather greenish, especially on the edges [No. 16].

§ 63. To discriminate bromides from chlorides more distinctly, the bromide is fused with bisulphate of potassa, both in the anhydrous state, in a small matrass with long neck. Sulphurous acid is evolved, and the matrass is filled with yellow vapors of bromine, characterized by their peculiar odor. The color of the gas is only clearly seen at daylight.

Cadmium.

The reactions of cadmium and its compounds, see §§ 11, 24, and Table II, 4.

§ 64. To detect a very small quantity of cadmium, one per cent. or less, in zinc or its ores, the pulverized assay is mixed with Sd and exposed for a short time to the R Fl on Ch. A distinct Ct of oxide of cadmium is deposited. The zinc being less volatile, evaporates only with continued blowing [No. 53].

Chlorine.

§ 65. Some oxide of copper is dissolved by means of the O Fl in a bead of S Ph on platinum wire, until it has assumed a deep-green color. Some grains of the pulverized assay [No. 18] are then made to adhere to the bead, and both heated with the blue cone of the flame. If chlorine is present the flame now assumes an intense azure-blue color, owing to the formation of chloride of copper (v. § 36). This test is very delicate, and will show the presence of a very minute quantity of chlorine.

§ 66. Another method is to place on silver-foil some protosulphate of iron, or some sulphate of copper, to moisten it with a drop of water, and then to add the assay [No. 18]. After a while the