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lye of caustic soda to a concentrated solution of perchloride of tin till the pre-cipitate which falls at first is all re-dissolved. It is then, of course, mixedwith the chloride of sodium. It may also be prepared in the dry way.Greenwood and Mercer obtain it by taking 22 lbs. of caustic soda (1 gallonweighing 13^ lbs.), and putting it in an iron crucible heated to low redness bya fire under it. When watery vapours cease to come off they add 8 lbs.nitrate of soda and 4 lbs. of common salt. When the whole is at or near thepoint of fusion 10 lbs. of feathered block tin are added and stirred with aniron rod until deflagration takes place, and the mass becomes fully red hotand of a pasty consistence. It may be purified by dissolving it, when cold, inwater, allowing impurities to settle, decanting off the clear liquids, andevaporating it down to near dryness.

Young heats finely ground tin ore of good quality along with caustic sodato about 6oo° F.; or with nitrate and muriate of soda (common salt), a currentof steam being passed at the same time over the mass. Purification bysolution in water and settling, and subsequent decantation and boiling downare here necessary.

Haeffely places in an iron pan litharge or red-lead (or hydrated peroxide ofiron, hydrated peroxide of manganese, manganate of soda, indigo, &c.) and asolution of caustic soda containing 22 per cent of alkali. A plumbate orplumbite of soda is thus formed, heat being applied to hasten the process, andthe air being as far as possible excluded. Feathered tin is then suspended orthrown into the liquid, when it dissolves, forming stannate of soda, whilstmetallic lead is thrown down in a spongy state. The proportions are—16 lbs.tin, 45 lbs. caustic soda at 70° Tw., and 70 to 80 of litharge, or 54 lbs. of red-lead. When the tin is perfe&ly dissolved, which may require four to fivehours boiling, the fire is withdrawn, and the sediment allowed to settle, andthe clear liquid is decanted, and is ready for use. The deposit of spongy leadmay be re-converted into litharge or red-lead by prolonged exposure to theair at a heat just below redness, and may be then used for another operation.

To ascertain the amount of tin present in a commercial sample of stannate,a small portion is dissolved in water, to which a few drops of hydrochloricacid have been added, and a few pieces of sheet zinc, pure and clean, are placedin the mixture. The tin is thus precipitated in a spongy metallic state. It iscollected, washed with distilled water, re-dissolved in pure hydrochloric acid,and its amount is determined as explained above.

Some dyers and printers believe that they can ascertain the value of astannate by dissolving a known weight in a fixed measure of water, and notingits specific gravity as shown on Twaddle’s hydrometer. This test is quitefallacious, since an adulterated article will raise the specific gravity of wateras well as one of the best quality. Manufacturers of spurious chemicals are,as a rule, inclined to appeal to the hydrometer as a test of value.

Stannate of soda may contain an excess of alkali as well as silica, &c., fromcareless workmanship, and it may be intentionally sophisticated with commonsalt. The percentage of water in a hydrated or crystalline stannate is from20 to 27 per cent. Salt is sometimes present to the amount of 28 per cent.

Stannate of soda is used in printing to prepare the cloth for receiving theso-called steam-colours. The calico is then passed through very dilute