MODERN USES OF THE METAL ALUMINIUM 627 



yeast in the very least {ibid. 1911), the yeast cell disregarding 

 the presence of aluminium salts exactly as the human stomach 

 does. This neutral property of aluminium, taken in conjunction 

 with the fact that its solubility in sound beer is extremely small, 

 have led to the rapid introduction of brewery plant made of 

 aluminium. 



The vessels used for this purpose are of exceptional size, 

 some of them holding 25,000 — 30,000 gallons of beer. To manu- 

 facture such tanks of aluminium was quite beyond the capacity 

 of manufacturers until very recently but new processes have 

 been evolved (to which reference will be made later) by which 

 vessels of this size can now be made and a new industry based 

 thereon has arisen. The accompanying illustrations show both 

 a fermenting tank made of aluminium and also a vessel in 

 which secondary fermentation takes place under pressure, the 

 carbon dioxide evolved being imprisoned and dissolved in the 

 beer. These tanks, which are being used in rapidly increasing 

 numbers, have to withstand considerable pressures, so that 

 their manufacture places no small demand upon the skill of 

 the makers. 



The second consideration which has led to the adoption of 

 aluminium in many cases is the fact that the salts of aluminium, 

 without known exception, are colourless. In this respect it 

 differs from practically all the other common metals used by 

 chemists. All the salts of copper and iron are coloured, whilst both 

 lead and tin easily give rise to discoloration. In many industries 

 this fact is of great importance, as it is often impossible to 

 prevent dissolution altogether and in such cases the certainty 

 that no discoloration will follow from the introduction into a 

 product of small quantities of the metal of which the containing 

 vessels are made is an obvious advantage. Many examples 

 might be quoted in illustration but two or three will suffice. In 

 making varnish, various gums, oils and resins are heated in 

 small metal pots, over a direct fire, at temperatures varying from 

 350 to 400 C. At this temperature, the lower boiling constituents 

 distil off but condense in part on the upper and cooler surface of 

 the vessel, thence flowing back into the main bulk of material ; 

 these volatile constituents often attack metals very freely and if, 

 as has been the practice, iron or copper vessels are used, the 

 condensate is brightly coloured — brown or green, as the case may 

 be. As one great object of the varnish maker is to obtain a 



