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This was the common potash alum and uncombined with any carbonated alkali, and it passed into the stomach unchanged.

Common alum is strictly potash alum; other two varieties are soda alum and ammonia alum, both similar in properties.

For example, episomorphs of white potash alum and violet chrome alum, of white magnesium sulphate and green nickel sulphate, and of many other pairs of salts, have been obtained.

Portions of the gum solutions were mixed with small quantities of menthol, thymol, salol, and saccharin in alkaline solution, also with boric acid, sodium phosphate, and potash alum in aqueous solution.

It is quite a matter of indifference to the photographer whether he uses potash alum or ammonia alum.