Platinum. Also called platina - is the heaviest substance but one (see No. 47) known, having a specific gravity of fully 21, which may be raised to about 21.5 by hammering. It is whiter than iron, harder than silver, infusible in the hottest furnace, and melts only before the compound blowpipe at a heat of about 3080° Fahr. On this account it is valuable for making capsules etc., intended to resist strong heat. Platinum undergoes no change by exposure to air and moisture, or the strongest heat of a smith's forge, and is not attacked by any of the pure acids, but is dissolved by chlorine and nitro-muriatic acid (aqua regia), though with more difficulty than gold. Spongy and powdered platinum possess the remarkable property of causing the union of oxygen and hydrogen gases. It is chiefly imported from South America, but is also found in the Ural Mountains of Russia, in Ceylon, and a few other places. Platinum, when alloyed with silver, is soluble in nitric acid; the pure metal is dissolved by aqua regia, and is more or less attacked by caustic alkali, nitre, phosphorus, etc.., with heat. Platinum is precipitated from its solutions by deoxidizing substances under the form of a black powder, which has the power of absorbing oxygen, and again imparting it to combustible substances, and thus causing their oxidation. In this way alcohol and pyroxilic spirit may be converted into acetic and formic acids, etc.. (See No. 1741 (To Make Alcohol Vinegar), also Acetic Acid.) (Cooley.)

3334. To Purify Platinum

3334.    To Purify Platinum. The native alloy (crude platinum) is acted upon, as far as possible, with nitro-muriatic acid, containing an excess of muriatic acid, and slightly diluted with water. The solution is precipitated by the addition of sal-ammoniac, which throws down nearly the whole of the platinum in the state of an ammonio-chloride, which is washed with a little cold water, dried, and heated to redness; the product is spongy metallic platinum. This is made into a thin uniform paste with water, pressed in a brass mould, to squeeze out the water and render the mass sufficiently solid to bear handling. It is then dried, carefully heated to whiteness, and hammered or pressed in the heated state; after this treatment it may be rolled into plates or worked into any desired shape. (Cooley).

3335. Platinated Asbestos

3335.    Platinated Asbestos. Dip asbestos in a solution of chloride of platinum, and heat it to redness. It causes the inflammation of hydrogen in the same manner as sponge platinum.

3336. Spongy Platinum

3336. Spongy Platinum. Dissolve separately crude bichloride of platinum, and hydrochlorate of ammonia in proof spirit; add the one solution to the other as long as a | precipitate falls; this is collected, and, while still moist, formed into little balls or pieces, which are then dried, and gradually heated to redness.

3337. Spongy Platinum

3337. Spongy Platinum. Dissolve platinum, by the aid of heat, in a mixture of three parts nitric and 5 parts muriatic acid, avoiding great excess of acid. To this solution add a strong solution of muriate of ammonia; collect the resulting precipitate on a filter, and, when nearly dry, form it into a mass of the shape desired for the sponge. Heat this to whiteness on charcoal, with a blow-pipe or otherwise, and the platinum remains in the spongy state. Its characteristic properties may be restored, when lost, by simply heating it to redness.

3338. Platinum-Black

3338. Platinum-Black. Platina Mohr. This is platinum in a finely divided state, and is obtained thus: - Add to a solution of bichloride of platinum, an excess of carbonate of soda, and a quantity of sugar. Boil until the precipitate which forms becomes, after a little while, perfectly black, and the supernatant liquid colorless; filter the powder, wash, and dry it by a gentle heat. Another method is by melting platina ore with twice its weight of zinc, powdering, digesting first in dilute sulphuric acid, and next in dilute nitric acid, to remove the zinc, assisting the action of the menstruum by heat; it is then digested in potash lye, and lastly in pure water, after which it is carefully dried. Platinum-black possesses the property of condensing gases, more especially oxygen, into its pores, and afterwards yielding it to various oxidizable substances. If some of it be mixed with alcohol into a paste, and spread on a watch glass, pure acetic acid is given off, and affords a ready means of diffusing the odor of vinegar in an apartment. (See No. 1741 (To Make Alcohol Vinegar).)