624 SCIENCE PROGRESS 



surface that it is possible to tell at a glance whether it be clean 

 or not. In addition to the fact that it dissolves but slowly in 

 weak organic acids is the immensely important fact that even 

 in solution it is entirely innocuous. Unlike tinned copper, 

 tinned iron and enamelled iron, it is uniform throughout its 

 thickness and consequently there is no coating to wear off, 

 crack or chip. Having these advantages, the question may well 

 be asked " How is it that its use is not universal ? " The 

 reasons are three in number. The cost of aluminium still 

 places it above the reach of the poorest ; the aluminium formerly 

 used for the purpose was inferior ; lastly, the metal cannot be 

 cleaned by the methods generally in use in the kitchen. 



The first of these statements need not detain us. 



The inferior metal formerly and still occasionally used 

 brought and brings its own nemesis. It was stated above 

 that the solubility of aluminium in weak organic acids is small 

 and if it took place generally over the surface of the metal, it 

 would be negligible. Unfortunately, however, this is not the 

 case. The presence of small impurities in the metal or even 

 of physical differences between adjacent particles, may lead to 

 local dissolution and pitting or perforation of the metal. Owing 

 to improvements in the methods of manufacture, the former 

 trouble has been largely obviated and since the recognition 

 of the importance of the physical state of the metal, still further 

 improvement may be looked for. As a matter of fact, the 

 degree of progress which has already been attained is very 

 remarkable. In America and in Germany, millions of cooking 

 utensils are made annually and 'the percentage of returns is 

 nowadays very small indeed. 



Now as to the third difficulty. 



Aluminium unfortunately is readily attacked by alkalis and, 

 therefore, the cleansing agent of the kitchen, soda, is one of 

 its worst enemies. As a consequence, the cleansing of aluminium 

 must be effected mechanically and entails appreciably more 

 labour than if effected in the customary manner by means of 

 alkali. This is the chief difficulty which remains to be over- 

 come. In Germany, where the "hausfrau" herself takes pride 

 in the appearance of her kitchen and herself does much of the 

 cooking, it has not been sufficient to counteract the obvious 

 advantages the metal has 4 One German factory known to the 

 writer used in 1910 about 3,000 tons of aluminium, almost all 



