Manchester Memoirs, Vol. xlv. (1901), No. 15. 9 



to a pressure of 100 cm,, and that when reduced to the 

 state of subdivision denoted by i cm. pressure the 

 sohibiHty is increased to 17-5 per cent. 



But this conclusion is fallacious if the specimen is a 

 mixture of two or more substances. The argument of the 

 authors is based upon the assumption that they are dealing 

 throughout with the same compound in different states of 

 subdivision. It has no validity if more than one compound 

 is present, since the solubilities found do not all relate to 

 the same substance. 



Now, it is well known that the more soluble kinds of 

 lead silicate are of softer texture than the more insoluble. 

 In the process of grinding a fritt which contains a small 

 admixture of such soluble silicate, this more soluble 

 portion will on account of its softness be ground to finer 

 dimensions than the bulk of the fritt. Consequently, when 

 the powder is separated into finer and coarser fractions by 

 elutriation, a great part of the soluble compound will be 

 found concentrated in the finer portions. These finer 

 portions will therefore show a solubility greater than the 

 average for the whole fritt, while the coarser fractions will 

 have a solubility less than the average ; which is precisely 

 what is shown by the experiments adduced by Messrs. 

 Jackson and Rich. 



Thus the experiments in question do not prove that 

 the differences of solubility obtained are due to mere 

 differences of dimensions of the particles. They can only 

 do this if the various fractions are shown to have the 

 same chemical composition, and on this point the authors 

 offer no evidence whatever. 



In the concluding section of their paper {loc. cit., pp. 

 12-13) the writers describe an experiment in which a 

 specimen of glaze was found to be continuously acted upon 

 by acid when mixed with pebbles and rotated for 22 hours 



