626 SCIENCE PROGRESS 



health of thousands of people, to say nothing of the reputation 

 and consequently the success of the manufacturer. Many 

 metallic salts, especially those of the heavy metals, act as 

 specific poisons on the human system but aluminium salts have 

 no such deleterious property. As it is not absorbed by the 

 mucous membrane of the stomach, aluminium has no chance 

 of exerting any objectionable effect, being rejected by the 

 system in toto (Stem. Dissertation Dor-path, 1886; Plagge u. 

 Lebbin. Veroff. des Militar. Sanitats Wesens, 1893 ; Herbert, Acad, 

 des Sciences, 1907, etc.). Thus it comes about that even if 

 aluminium were readily dissolved by foodstuffs, it would never- 

 theless be harmless. But we have seen already that aluminium 

 is but very slightly attacked by weak organic acids, so that the 

 use of this metal is attended with complete safety. 



In this respect, aluminium stands pre-eminent among the 

 metals, its only rival being perhaps tin, which owes its popularity 

 to its insolubility in weak acids. Once formed, however, its 

 salts are poisonous. But tin, in addition to its costliness, is 

 deficient in the mechanical properties which are required for the 

 construction of large chemical plant. It is, therefore, generally 

 used only as a thin coating on other metals — copper, lead or iron. 



In this connexion, reference may be made to one particular 

 living organism towards which aluminium is entirely inactive, 

 namely, yeast, a property which renders the metal one of extreme 

 importance to brewers. Brewing is an industry which is carried 

 on under the most stringent conditions of asepticism. The 

 demands made upon the modern brewer are such that foreign 

 organisms of every kind have to be excluded rigidly, the most 

 painstaking precautions being taken to attain this end. One of 

 these is the gradual elimination of wooden vessels, which on 

 account of their porosity tend to harbour bacteria and are 

 cleansed with difficulty. In place of wood, both copper and 

 enamelled iron have been used but it has been found (Chapman, 

 Journal 0/ the Institute of Brewing, 1909) that under certain con- 

 ditions copper is dissolved by beer worts at the air- water line and 

 that the copper which enters into solution affects in a very marked 

 extent the reproductive power and fermentative vigour of yeast. 

 Enamel is free from this objection but it is easily damaged, so 

 that the iron subsurface becomes exposed and rusts, so affecting 

 both the taste and the brilliancy of beer. 



Chapman has shown that the salts of aluminium do not affect 



