128 Mr. S. U. Pickering on the Diffusion 



that the mouth of the inner jar should be exactly level. The 

 jars were marked so that they could be replaced in the proper 

 position after being filled. When filled they were closed by 

 glass plates with rods attached to them, and then lowered 

 inside the larger jars which had previously been filled with 

 water. The glass plates were then removed very slowly and 

 carefully. At the end of the time allowed for diffusion the 

 plates were replaced on the jars, the latter were removed from 

 the water and the strength of their contents determined. Both 

 the large and small jars were filled two days before the latter 

 were placed inside the former, in order that the temperature 

 of the cellar in which the determinations were made might be 

 attained; and after the inner jars had been placed in position 

 a further period of five hours was allowed before the glass 

 plates were removed, so that any disturbance of temperature 

 which had occurred in placing them in position might subside. 



The capacity of the inner jars was 480 cubic centim., their 

 internal diameter was 70 millim., and their internal height 

 125 millim. About three dozen of them were made, and of 

 these the twelve which were found to be most uniform in size 

 were used in the determinations. The extreme difference in 

 the capacity of the largest and smallest of these twelve was 

 3*3 per cent., and the extreme difference of their superficies 

 at the mouth was 3*8 per cent. The outer jars contained 

 12^000 cubic centim. of water, or twenty-five times the 

 volume of the inner jars. The mouths of the jars were about 

 midway between the surface and bottom of the water in the 

 inner jnrs. 



The strength of the solutions remaining in the jars at the 

 end of the experiments w r as determined by means of their 

 freezing-points. The solutions taken to start with were made 

 up by weighing. The freezing-points of these, and also of 

 weaker solutions obtained from them by dilution, were deter- 

 mined, and from these results the strength of any solution 

 having a given freezing-point could be calculated. In order 

 to minimize any errors due to possible irregularities of the 

 freezing-points when plotted against composition, the solutions 

 of known strengths, of which the freezing-points were deter- 

 mined, were selected so as to approach as nearly as possible 

 to the strength of the solution left in the diffusion-jar. 



The strength of the solutions taken was, as a rule, about 

 0*3 molecule to every 100 molecules of water, showing a 

 depression of the freezing-point of water amounting to about 

 o, 3 ; about one third of the dissolved substance had diffused 

 out by the end of the determination, the decrease in the 





