two assays should always be made, exposing the substance first to the action of the O Fl and then to the action of the R Fl. The following bodies undergo, when submitted to this treatment, characteristic changes.

§ 20. Arsenic: It is volatilized without previous fusion, the Ch is covered with a white Ct, which is far distant from the assaypiece, and which is produced by both the O Fl and R Fl; the Ct is very volatile, and is easily driven away by the Blp flame, emitting the peculiar alliaceous odor characteristic of arsenic [No. 42].

§ 21. Antimony: It enters readily into fusion and covers the Ch with white oxide; the ring is not so far distant from the assaypiece as in the case of arsenic; it may be driven away by the Blp flame, but is not so volatile as that of arsenic, and does not emit an alliaceous odor. Metallic antimony, when fused on Ch and heated to redness, remains a considerable time in a state of ignition without the aid of the Blp, disengaging, at the same time, a thick white smoke, which is partly deposited on the Ch around the metallic globule in white crystals of a pearly lustre [No. 41].

§ 22. Bismuth: It fuses readily in both flames and covers the Ch with oxide, which is dark orange-yellow while hot and lemonyellow when cold. The yellow Ct is usually surrounded by a white ring, consisting of carbonate of bismuth. The Ct is somewhat nearer the assay than that of antimony; it may be driven away by both flames; but the oxide of antimony, when played upon with the R Fl, imparts to the flame a greenish-blue tinge, which the oxide of bismuth does not [No. 43].

§ 23. Lead: It fuses easily and coats the Ch in both flames with oxide, which is dark lemon-yellow while hot and sulphuryellow when cold; in thin layers it is bluish-white and consists of carbonate. The Ct is found at the same distance from the assay as that of bismuth; it may be driven away by both flames; when played upon with the R Fl it imparts to the flame an azure-blue color [No. 11].

§ 24. Cadmium: It fuses readily; exposed to the O Fl it burns with a dark-yellow flame, emitting brown fumes of oxide which cover the Ch around the assay. This Ct is very characteristic; it is, when cold, of a reddish-brown color, in thin layers orange-yellow;

it is easily volatilized by both flames, without imparting a color to them [No. 44].

§ 25. Zinc: It fuses readily; exposed to the O Fl it burns with an intensely luminous greenish-white flame, emitting at the same time a thick white smoke which, partly condensing on the Ch, covers it with oxide, yellow while hot and white when cold. The Ct when played upon with the O F1 becomes luminous, but does not disappear [No. 46].

§ 26. Tin: It fuses readily; exposed to the O Fl it is converted into oxide, which may be blown away and thus be made to appear as a Ct; it is always found closely surrounding the assay-piece, is slightly yellow and luminous while hot, white when cold, and nonvolatile in both flames. Exposed to the R Fl the molten metal retains its bright metallic aspect [No. 13].

§ 27. Silver: When exposed for a long time to the action of the R Fl it yields a slight dark-red Ct of oxide [No. 45].

§ 28. Selenium: It fuses very readily in both flames with disengagement of brown fumes; at a short distance from the assay a steelgray Ct of a feeble metallic lustre is deposited; played upon with the R Fl it disappears with emission of a strong odor of rotten horse-radish, at the same time imparting to the flame a fine blue color [No. 87].

§ 29. Tellurium: It fuses very readily and coats the Ch in both flames with tellurous acid; the Ct is not very far distant from the assay; it is of a white color with a red or dark-yellow edge; played upon with the R Fl it disappears, imparting to the flame a green tinge.

§ 30. Besides the above named metals there are some other substances which, when treated before the Blp upon Ch cover it with coatings, which may be driven away when played upon with the O Fl, and which show in many cases a great resemblance to the Ct produced by antimony. Among the bodies possessing this property the following are the most frequently occurring ones:

The sulphurides of potassium, sodium, and lithium.

Thé chlorides of ammonium, potassium, sodium, and lithium. The chlorides of mercury, antimony, zinc, cadmium, lead, bismuth, tin, and copper.

The bromides and iodides of potassium and sodium.

Examination in the Platinum-pointed Pincers.

§ 31. This experiment serves a double purpose. It acquaints us with the degree of fusibility of the assay, and shows the presence or absence of such substances which possess the property of imparting to the flame a peculiar color. Many metals, the sulphurides, and some other compounds act upon metallic platinum at a high temperature; the fusibility, &c., of such substances ought to be tested on Ch. Others, again, fuse so easily that they cannot be held a sufficiently long time between the pincers to observe the color which they impart to the flame; they are most conveniently attached to the hook of the platinum wire, which is best done by heating the wire to redness and then touching the powder of the assay with it; a sufficient quantity generally remains adhering to the wire.

Some minerals decrepitate violently as soon as they are touched with the flame; in such cases, Berzelius advises to powder the substance very finely in an agate-mortar with addition of a little water, to place one or two drops of the mixture on a piece of Ch, and to gently heat it by means of the Blp flame until the mass lies loosely upon the Ch; it may then be taken up and held by the pincers. The same process is advantageously employed with substances which fuse only at a very high temperature. In all other cases the substance is roughly powdered and a thin piece which shows prominent edges selected for the experiment.

The assay is exposed to the action of the inner cone of the flame, when the outer cone may exhibit the following changes of color: § 32. 1. Yellow.

Soda and its salts cause an enlargement of the outer flame, and impart, at the same time, an intense reddish-yellow color [No. 18]. The presence of other substances which also possess the property of coloring the flame, but not in so high a degree, does not prevent the reaction. Silicates containing soda, exhibit the same phenomenon to a smaller or greater extent, according to their degree of fusibility and the amount of soda which they contain [No. 62]. With many salts of soda, which do not exhibit the reaction very

distinctly, it can be produced by mixing the salt with some chloride of silver to a paste (v. § 5), fastening it to the hook of a thin ironwire, and then exposing it to the action of the inner flame.

§ 33 2. Violet.

Potassa and many of its salts impart to the outer flame a distinct violet color [No. 15]. The presence of a small quantity of a salt of soda or lithia prevents the reaction. An addition of chloride of silver favors the reaction with the carbonate, nitrate, and some other salts of potassa.

§ 34. 3. Red.

Lithia and its salts impart to the outer flame a fine carmine-red color [No. 63]; the chloride of lithium shows the reaction better than any other salt. The presence of a salt of potassa does not prevent the reaction; the presence of even a small quantity of a salt of soda changes the color to yellowish-red. An addition of chloride of silver favors the reaction with many salts of lithia.

Chloride of strontium and some other salts of strontia, ex. gr. the carbonate and the sulphate, color the outer flame, immediately or after a while, carmine-red [No. 57]. The presence of baryta prevents the reaction. The carbonate and sulphate of strontia show the reaction remarkably well when mixed with chloride of silver and heated on iron-wire (v. § 5).

Chloride of calcium, calcareous spar, many compact limestones, and fluor-spar, color the outer flame, immediately or after a while, red; the color is not so intense as that produced by strontia. Gypsum and anhydrite impart at first a pale yellow, afterwards a red color of little intensity [No. 56]. An addition of chloride of silver usually increases the intensity of the color.

§ 35. 4. Green.

Chloride of barium, carbonate and sulphate of baryta, color the outer flame yellowish-green. The presence of lime does not pre vent the reaction [No. 58]. An addition of chloride of silver makes the color much more intense.

Oxide of copper and some of its salts, ex. gr. the carbonate, sulphate, and nitrate, impart to the outer flame a fine emeraldgreen color. Iodide of copper and some silicates containing copper, ex. gr. dioptase and chrysocolla, act in the same manner [No. 73]

An addition of chloride of silver produces increased intensity

of color.

Phosphoric acid, phosphates, and minerals containing phosphoric acid, impart to the outer flame a bluish-green color [No. 3].

Boracic acid colors the outer flame yellowish-green (greenfinch color) [No. 5]; if a small quantity of soda is present the color is mixed with yellow.

Molybdic acid, oxide of molybdenum, and the native sulphide of molybdenum, color the outer flame yellowish-green, like baryta [No. 83].

Tellurous acid enters into fusion, emits white fumes, and colors the outer flame green.

§ 36. 5. Blue.

Arsenic and some arsenides, ex. gr. smaltine and copper-nickel [No. 82] when heated on Ch impart a light-blue color to the outer flame. Some arsenates, ex. gr. scorodite and cobalt bloom, exhibit the same phenomenon in the pincers.

Antimony, fused on Ch in R Fl is surrounded by a very feeble bluish light [No. 41].

Metallic lead, fused on Ch in R Fl is surrounded by an azureblue light. Many salts of lead, heated in the pincers or on platinum wire, impart an intense azure-blue color to the outer flame [No. 11].

Chloride of copper colors the outer flame intensely azure-blue; after a while the color becomes green, owing to the formation of oxide of copper [No. 37].

Bromide of copper colors the outer flame greenish-blue; after a while the color changes to green.

Selenium, fused on Ch in R Fl vaporizes with an azure-blue light.

Examination with Borax and Salt of Phosphorus.

§ 37. The examination of the assay with borax and salt of phosphorus is eminently adapted to detect the presence of metallic oxides, a great number of them possessing the property of being at a high temperature dissolved by these fluxes with a peculiar color. Unoxidized metals and metallic sulphides, arsenides, &c., differ in this respect very materially from the pure oxides; hence