Alum

is used in many proce es—in the preparation of paper for water-colour painting, and of lakes, and carmine, from cochineal. Roche alum, or roach alum, Roman alum, and Turkey alum, are varieties of the common alum, described by med iæval writers as a lumens. Alumen (Lat.), Greek, ( stypteria ). Mediæval writers confused this word with the alums. The name was applied by the cla ics to several salts of the nature of vitriols, and among them to the natural sulphate of iron ( copperas or green vitriol of commerce).