XX 



axiom, so to speak, was not a science ; and as one proposition after another 

 arises out of it, the first idea itself appears grander and grander. Dalton, 

 like Newton, used the term atom as meaning a particle which could not be 

 divided by any force. But there seems no need to say that it could not be 

 divided by the imagination or even by new forces, in which case it becomes 

 the practical as opposed to the theoretical atom. Under the present 

 chemistry there probably exists another which shall deal with the broken 

 atom of our present science ; we do not know how many layers there may 

 be under it. It is strange that Dalton's idea was so purely mechanical, 

 although illustrating a purely chemical act : there is no talk of obscure 

 forces ; it is a movement like a carpenter's, a fitting of pieces in the manner 

 of a workman. Graham took up the subject in the same spirit, and seems 

 to have during his whole life sought for nothing beyond the knowledge of 

 the constitution of matter, and the mode in which the atoms or molecules 

 move. His favourite word is molecule, not atom ; indeed he seems too 

 guarded to use the latter in any case of measurable movement. His destiny 

 was to follow the progress of the molecule, and to show that there were 

 movements in bodies which depended on that aggregration of atoms, whether 

 ultimate atoms or not. "Whilst Dalton showed the relative weights of the 

 combining quantities, Graham showed the relative magnitude of groups 

 into which they resolved themselves. 



Having discovered that solid bodies could be divided into two classes, 

 colloid and crystalloid, and that the first consist of substances existing in 

 great varieties of conditions, and apt to undergo long and remarkable pro- 

 gressive changes, he seems to have taught us the way to obtain many sub- 

 stances practically new, although nominally such as we have seen. "Whilst 

 one, the colloid, has power of motion in itself to a considerable extent, the 

 other, the crystalloid, has power of motion in solutions, so that we are 

 introduced to a series of new forces, the end of which is not in the faintest 

 way foreseen. The door by which we enter these strange regions is found 

 by a series of the most uninviting trials ; it seems to have been hidden 

 uuder the most homelv brushwood, and few would think of toiling so lone; 

 in such a field. 



It may be well to go over some of his principal papers, and to observe 

 how constantly he kept to these ideas whilst penetrating further into the 

 subjects. 



In 1827 he observed that phosphate of magnesia effloresced very readily ; 

 this, he argued, proved a weak affinity for water ; if weak, heat ought to 

 destroy it, and so he found that it was thrown down anhydrous on boiling. 

 He argues that it is only the hydrate that is soluble, properly speaking, in 

 other cases also. 



This led him, in 1835, to examine the hydrate, when he found that 

 the tendency of phosphate of soda to combine with an additional dose of soda 

 was connected with the existence of closely combined water. This induced 

 him to separate the water of salts into two parts, crystalline and basic, the 



