Take 200 lbs. of kaolin, or any other aluminous clay in powder, and 70 lbs. of salt, dissolved in 100 parts of water to mix with the former ; the water is evaporated in a lead basin, and the mixture carried to a reverberato-ry iurnace heated to a dull red. color. After in hour's exposure in the fire the clay is taken out and treated, while hot, in lead basins with double its weight ot sulphuric acid at 40'',' the precaution being taken not to prolong the operation, or there would be danger of the lead melting. The yellow magpja thus obtained is placed in a re verberatory furnace, where it is heated from 200 to 250 (centigrade) , until it becomes white ; it is then taken out and treated with water in a leaden boiler. The soda alum is easily dissolved, and in the course of a few hours, when the liquid has entirely settled it is poured off.by means transferred into reservoirs, where it crystallizes at the end of the second day. The calcined earth might likewise be treated immediately with sulphuric acid, and the salt added only a short time before the end of the operation. But the first-named process is preferable. Whatever process is employed chlorohydric acid is disengaged, which, in a manufactory of any size, ought to be collected by the same means as is employed for the purpose in the manufacture of soda.
This article was originally published with the title "To make Crystallized Soda Alum"