ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



555 



In order to collect the spent polishing materials, the disc is surrounded 

 by a catcher C, which can be easily removed for cleaning. Into the top 

 of the catcher is fitted a guard ring 1), which being wide forms a rest for 

 the hand, and by being continued downwards below the surface of the 

 disc and nearly touching the edge, prevents any specimens that are being 

 polished from falling into the catcher should they be let slip from the 

 fingers. 



The standard machine is supplied with a switch H and flexible con- 

 necting wire, with a plug adapter attached, so that it can be connected 



Fig. 69. 



with any ordinary electric lamp fitting. The motor can be supplied suit- 

 able for any direct current circuit between 100-220 volts, or can be 

 specially made to run on an alternating circuit if desired. 



Metallography, etc. 



Spontaneous Disintegration of Aluminium.* — H. le Chatelier de- 

 scribes the microstructure of aluminium utensils in different stages of 

 disintegration. The metal in which the change had made progress 

 showed, after etching, a continuous cellular network. At the surface, 

 where the decay had proceeded the furthest, the network had developed 

 into actual spaces, separating the grains, which could easily be detached. 

 The disintegration appeared to be the result of the parting of the grains 

 at their boundaries. 



The same author! further discusses the subject. Investigations by 

 Heyn and Bauer have shown that the decay takes place only in severely 

 cold-worked metal. The instability of cold-worked metals appears to be 

 a general phenomenon, and should not be overlooked when additional 

 strength is sought by cold-working. While chemical influences may 

 play a part in the decay of such material, they probably act merely as 

 exciting agencies, setting in operation the latent tendency to disintegrate. 



* Comptes Rendus, clii. (1911) pp. 650-2 (4 figs.), 

 t Rev. Metallurgie, viii. (1911) pp. 373-6 (4 figs.). 



