264 Prof. Graham on the Diffusion of Liquids. 



numerical relations are known to prevail in the diffusion velo- 

 cities of. the gases, from which their densities are deducible. 



It was desirable to make numerous simultaneous observa- 

 tions on the salts compared, in order to secure uniformity of 

 conditions, particularly of temperature. The means of greatly 

 multiplying the experiments were obtained by having the so- 

 lution 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), Yip. 3. 

 holding about 4 ounces, or more nearly 2080 grs. of f~~> 

 water to the base of the neck, and the mouths of all J I 

 were ground down, so as to give the phial a uniform 

 height of 3*8 inches. The mouth or neck was also 

 ground to fit a gauge-stopper of wood, which was 

 0.5 inch deep and slightly conical, being 1*24 inch 

 in diameter on the upper, and 1*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 di- 

 stance 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 Fig. 4. 



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 before 

 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 inch. This water atmosphere 

 amounted to 8750 grs., or about 20 ounces. 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 men- 

 tioned. 



II. Diffusion of Salts of Potash and Ammonia. 



Solutions were prepared of the various salts, in a pure state, 

 in certain fixed proportions, namely, 2, 4, 6§ 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 tempera- 





