190 PROFESSOR THOMAS GRAHAm's SCIENTIFIC WORK. 



to 2.350 at 70°; and correlatively the transpiration times were found to 

 decrease in the same i)roportiou. The results obtained with alcohol 

 were precisely similar. 



IV. 



Diffusion of liquids. — Mr. Graham's early study of the spontaneous 

 movements of gases, so as to mix with one another, naturally led him 

 to investigate the similarly occurring movements of liquids. His results 

 formed the subject of two papers communicated to the Eoyal Society, 

 one in 1849, "On the diffusion of liquids,"* and the other in 1801, " On 

 liquid diffusion applied to analysis."! In the series of experiments 

 described in the first of these papers and in two supplementary com- 

 munications an open, wide-mouthed vial, filled with a solution of some 

 salt or other substance, was placed in a jar of water ; when, in course of 

 time, a portion of the dissolved salt, described as the diffusate, passed 

 gradually from the vial into the external water. By experimenting iu 

 this manner, the amounts of diffusate yielded by different substances 

 were found to vary greatly. Thus, under i^recisely the same conditions, 

 common salt yielded twice as large a diffusate as Epsom salt, and this 

 latter twice as large a diffusate as gum-arabic. Every substance ex- 

 amined was in this way found to have its own rate of diffusibility in the 

 same liquid medium — the rate varying with the nature of the medium — 

 whether water or alcohol, for instance. It is noticeable that the method 

 of vial diffusion resorted to in these experiments is exactly similar to 

 that employed by Mr. Graham in his earliest experiments on the diffu- 

 sion of gases, published in the (Quarterly Journal of Science for 1829. 



In the series of experiments recorded in the paper "On liquid diffu- 

 sion applied to analysis," the solution of the salt to be diffused, instead 

 of being placed in a vial, was conveyed by means of a pipette to the 

 bottom of a jar of water ; when, in course of time, the dissolved salt 

 gradually rose from the bottom, through the superincumbent water, to 

 a height or extent i)roportional to its diffusibility. The results of this 

 method of jar-diffusion were found to bear out generally those attained 

 by the nu'thod of vial-diffusion ; while they further showed the absolute 

 rate or velocity of the diffusive movement. Thus, during a fourteen 

 days' aqueous diffusion from 10 per cent, solutions of gum-arabic, 

 Epsom salt, and common salt respectively, the gum-arabic rose only 

 through y"j of the superincumbent water, or to a height of 55.5 milli- 

 meters ; the Epsom salt rose through the whole \^ of superincumbent 

 water, or to a height of 111 millimeters ; and the common salt not only 

 rose to the top, but would have risen much higher, seeing that the up- 

 permost or fourteenth statum of water, into which it had diffused, con- 

 tained about fifteen times as much salt as was contained in the upper- 

 most or fourteenth stratum of water into Avhich the Epsom salt had 

 diffused. 



* Pliilosophical Transactions, 1850, pp. 1, 805 ; 1B51, p. 483. 

 + Ibid., 1861, p. 183. 



