White alum

The substances used for cleaning and roughening the surface of the stone so as to facilitate the absorption or adherence of the color are various. Alum, which doubtless comprised as with Dioscorides and Pliny salts of iron as well as of aluminum, is frequently used, although white alum is here often specifically mentioned. Urine is frequently used, its efficiency being doubtless due to the carbonate of ammonium formed on standing. Limewater, sodium carbonate, vinegar, and a solution of sulphur and lime (polysulphides of calcium) are other constituents of the mordanting solutions. 

The porous is better, and is full of hollow pipes, like the sponge. It more nearly approaches white, with a certain fattiness, is devoid of sand or grit, and is easily crumbled. It is neither as black as that of Egypt nor as white as the celebrated White Alum of Melos. 

Blue Hungarian Copperas combined with a very white Alum. 

Potassium Aluminum Sulfate. Potassium aluminum sulfate [7784-24-9]. KAl(SO 12H20, is a white, astringent crystal known as potassium alum, ordinary alum, or potash alum. Its formula weight is 474.39 mp 92.5 °C sp gr 1.75 and solubiUty 11.4 g per 100 mL H2O at 20°C (8). It is soluble in dilute acid and insoluble in alcohol. It dehydrates at about 200 °C to porous desiccated potassium alum [10043-67-1], KAl(SO dried or burnt alum, which has a formula weight of 258.20. 

The commercial dry alum most often used in wastewater treatment is known as filter alum, and has the approximate chemical formula A 12(804)3 T4H2O and a molecular weight of about 600. Alum is white to cream in color and a 1 percent solution has a pH of about 3.5. The conunercially available grades of alum and their corresponding bulk densities and angles of repose are given in Table 1. 

Mineral tanning was probably first practiced in ancient Mesopotamia and then spread to Egypt, the Middle East, and the Mediterranean Sea area (Levey 1958). Mineral-tanned leather is soft to handle, has a velvety texture, and is almost white, a color practically impossible to achieve by other tanning processes. It is, however, very sensitive to humidity and water under wet conditions the alum in the leather is hydrolyzed (decomposed by water), forming sulfuric acid, a very strong acid that attacks the leather and causes its rapid decay. Mineral-tanned leather that has been humid or wet for a more or less extended period of time loses some of its characteristic properties, such as softness, pliability, and strength, and becomes hard, horny, and brittle. 

Father Athanasius Kircher said that the phosphorus was made by pulverizing the Bologna stone, mixing it with white of egg or linseed oil, and calcining it in a special furnace. He found specimens in the alum mines at Tolfa (59). Biographical sketches of Father Kircher were published in The Hormone in 1934. (109) and in the Journal of Chemical Education in 1955 (139). 

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