178 PEOFESSOR THOMAS GRAHAm's SCIENTIFIC WORK. 



was entitled "A short account of experimental researches on the diffu- 

 sion of gases through each other, and their separation by mechanical 

 means." In the same year, he became lecturer on chemistry at the 

 Mechanics' Institute, Glasgow ; and in the next year, 1830, achieved 

 the yet more decisive step of being appointed professor of chemistry at 

 the Andersonian University. By this appointment he was relieved from 

 anxiety on the score of living, and afforded, in a modest way, the means 

 of carrying out his experimentnl work. 



In 1831 he read, before the Royal Society of Edinburgh, a paper " On 

 the law of the diffusion of gases," for which the Keith prize of the society 

 was shortly afterward awarded him. Although several of his earlier 

 papers, and especially that " On the diffusion of gases," j)ublished in 

 the Quarterly Journal of Science, had given evidence of considerable 

 power, it was this paper — in which he established the now well-recog- 

 nized law that the velocities of diffusion of different gases are inversely 

 as the square roots of their specitic gravities — that constituted the first 

 of what may properly be considered his great contributions to the 

 progress of chemical science. 



In 1833 he communicated a paper of scarcely less importance, to the 

 Eoyal Society of London, entitled " Researches on the arseniates, phos- 

 phates, and modifications of pliosphoric acid." It afforded further evi- 

 dence of Mr. Graham's quiet, steady power of investigating phenomena, 

 and of his skill in interpreting results ; or rather of his skill in setting 

 fortli the results in all their simplicity, undistorted by the gloss of 

 preconceived notions, so as to make them render up their own in- 

 terpretation. It is difficult nowadays to realize the independence of 

 mind involved in Mr. Graham's simple interpretation of the facts 

 j)resented to him in this research, by the light of the facts themselves, 

 irrespective of all traditional modes of viewing them. Their investiga,- 

 tion let in a flood of liglit upon the chemistry of that day, and formed 

 a starting-point from which many of our most recent advances may be 

 directly traced. In this paper, Mr. Graham established the existence 

 of two new, and, at that time, wholly unanticipated classes of bodies, 

 namely, the class of polybasic acids and salts, and the class of so-called 

 auhydro acids and salts. The views of Graham on the polybasicnty of 

 phosphoric acid were soon afterward applied by Liebig to tartaric 

 acid, and by Gerhardt to polybasic acids in general, as we now recog- 

 nize them. After a long interval, the idea of polybasicity was next ex- 

 tended to radicals and to metals by Williamson and myself successively; 

 afterward to alcohols by Wurtz, and to ammonias by Hofnmnn. The 

 notion of anhydro-salts was extended by myself to the different classes 

 of silicates ; by Wurtz to the comi)c)unds intermediate between oxide of 

 ethylene and glycol ; and by other chemists to many different series of 

 organic bodies. 



The next most important of the researches comj)leted by Mr. Gra- 

 ham while at Glasgow was the subject of a pamper communicated to the 



