PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
25 
produced by liquid as well as by gaseous diffusion. But it still remains to be found 
whether the diffusibilities of different salts are in any fixed proportion to each other, 
as simple numerical relations are known to prevail in the diffusion velocities of the 
gases, from which their densities are deducible. 
It was desirable to make numerous simultaneous observations on the salts com- 
pared, in order to secure uniformity of conditions, particularly of temperature. The 
means of greatly multiplying the experiments were obtained by having the solution 
phial cast in a mould, so that any number of solution cells could be procured of the 
same form and dimensions. The phials were of the form represented (fig. 3), pjg 3 
holding about 4 ounces, or more nearly 2080 grs. of water to the base of the 
neck, and the mouths of all were ground down, so as to give the phial a uni- 
form height of 3‘8 inehes. The mouth or neck was also ground to fit a gauge- 
stopper of wood, whieh was 0'5 inch deep and slightly conical, being T24 
inch in diameter on the upper, and T 20 inch on the lower surface. These 
are therefore the dimensions of the diffusion aperture of the new solution cells. 
A little contrivance to be used in filling the phials to a constant distance of half an 
inch from the surface of the lip, proved useful. It was a narrow slip of brass plate, 
having a descending pin of exactly half an inch in length ^ 
fixed on one side of it (fig. 4). This being laid across the 
mouth of the phial with the pin downwards in the neck, 
the solution was poured into the phial till it reached the 
point of the pin. The brass plate and pin being removed, 
the neck was then filled up with distilled water, with the aid of the little float as be- 
fore described. The water-jar, in which the solution phial stood, was filled up with 
water also as formerly, so as to cover the phial entirely to the depth of 1 ineh. This 
water atmosphere amounted to 8/50 grs., or about 20 ounees. A glass plate was 
placed upon the mouth of the water-jar itself to prevent evaporation. Sometimes 80 
or 100 diffusion cells were put in action at the same time. The period of diffusion 
chosen was now always exactly seven days, unless otherwise mentioned. 
II. DIFFUSION OF SALTS OF POTASH AND AMMONIA. 
Solutions were prepared of the various salts, in a pure state, in certain fixed pro- 
portions, namely, 2 , 4, 6 f and 10 parts of salt to 100 parts of water by weight. The 
density of these solutions was observed by the weighing-bottle, at 60°. The solutions 
were frequently diffused at two different temperatures ; one, the temperature of the 
atmosphere, which was fortunately remarkably constant during most of the experi- 
ments to be recorded at present, and the other, a lower temperature, obtained in a 
close box of large dimensions, containing masses of ice. The results at the artifieial 
temperature were obviously less accurate than those of the natural temperature, but 
have still considerable value. Three experiments were generally made upon the diffu- 
sion of eaeh solution at the higher, with two experiments at the lower temperature. 
MDCCCL. 
E 
