potash alum

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

The rule indicates, also, that aluminium chloride would be better than the sulphate or than potash alum.

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

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