ACTIONS AND USES 221 



sulphate. They are found in limited quantity on the surface 

 of soils and rocks, especially in volcanic districts, and are 

 largely prepared from aluminium clay, shale, or schist, which 

 mainly consists of aluminous silicate and iron sulphide. 

 Near Paisley, where alum is extensively manufactured, the 

 schist lies between the coal and limestone strata. When 

 slowly roasted it absorbs oxygen, and the sulphur is con- 

 verted into sulphuric acid, which unites with the iron and 

 aluminium. Water is added, and a large portion of the less 

 soluble iron sulphate crystallises out. 



To make potash alum this residual solution is treated 

 with potassium chloride, usually obtained as a by-product 

 from the soap-boilers, saltpetre refineries, and glass- 

 houses ; double decomposition results. The remaining iron 

 sulphate is converted into iron chloride, which continues in 

 solution ; while potassium sulphate unites with aluminium 

 sulphate to form potash alum, which crystallises, and is 

 further purified by repeated solution and crystallisation. 



PROPERTIES. The alums occur in transparent, colourless 

 cubes, or octahedral crystals, have a sweet, acidulous, astrin- 

 gent taste, act like acids on colouring matter, and, when 

 heated, fuse and part with their water of crystallisation. 

 They are soluble in one-third of their own weight of water 

 at 212 Fahr., and in seven parts of cold water. Freely 

 soluble in glycerin : insoluble in alcohol. 



ACTIONS AND USES. Alum is slightly irritant, astringent, 

 and antiseptic, and is chiefly used externally as an astringent 

 styptic, desiccant, and caustic. 



Toxic EFFECTS. One or two ounces given to dogs cause 

 vomiting. But when the oesophagus was tied, and vomiting 

 prevented, Orfila found that two ounces occasioned death in 

 five hours, with great exhaustion ; the intestines were found 

 extensively inflamed. Devergie found that four drachms 

 of dried alum killed a dog when the gullet was tied. An 

 ounce introduced into the areolar tissue of a dog's thigh 

 caused excessive suppuration, and death in fifteen hours. 

 Moiroud states that large doses given for some time exhaust 

 the digestive organs, diminish cutaneous transpiration, and 

 produce grave disorders. Several ounces given daily to 

 cows, and continued for a week or two, do not produce any 



