460 MODERN CHEMISTRY. 



more exact knowledge ; a fact especially to be noted in 

 some of his applications of chemistry to animal physiology. 

 It is the single deduction we have to make from the merits 

 of his various labours. 



Had we space for it, many other attainments of modern 

 Chemistry might be named, all hanging upon the same great 

 principle. Such are the relations of combining volumes of 

 gases to their atomic weights ; the peculiar phenomena of 

 catalysis and of nascent gases ; the observations of Dulong, 

 Petit, Neumann, &c., on the relation between the specific 

 heat of bodies and their atomic weights; the facts con- 

 nected with allotropy and the curious mutual actions of like 

 atoms, well illustrated by Brodie ; and the bold specula- 

 tion of Dumas, representing what may be termed chemical 

 atoms (those which enter primarily into chemical combina- 

 tion) as themselves made up of groups of molecules, and 

 divisible into sub-multiple parts ; an hypothesis suggested 

 to meet difficulties as to the Hydrogen unit in the scale of 

 Atomic weights. 



A more particular mention is due to the remarkable re- 

 searches of Mr. Graham (Master of the Mint), which may 

 almost be said to offer a new mode of Chemical analysis to 

 our knowledge. Begun twelve years ago by experiments 

 on saline liquids and on gases, these researches have lately 

 been much extended, and their principle developed in a 

 paper presented to the Royal Society (Nov. 1861), "On 

 Liquid Diffusion applied to Analysis." The term of Dialysis 

 might fitly be used here, since the actual agent in separation 

 of the constituents of a chemical solution is simply well- 

 sized letter paper, through which permeation takes place. 

 This paper is not porous enough to act as a filter, or give 

 passage to the mixed fluid as a whole ; but it transmits cer- 

 tain molecular parts of these solutions, and thereby effects a 

 real chemical decomposition, by means almost mechanical 



