|<|Q lloyal Society. 



the experiments, the results did not vary more than l-40th part. 

 The proportion of salt which diffused out in such experiments 

 amounted to about l-8th of the whole. 



Secondly, that the proportion of salt diffused increases with the 

 temperature ; an elevation of 80° Fahr. doubling the quantity of 

 chloride of sodium diff"used in the same time. 



The diffusibility of a variety of substances was next compared, 

 a solution of 20 parts of the substance in 100 water being always 

 used. Some of the results were as follows, the quantities diffused 

 being expressed in grains : chloride of sodium 58"68, sulphate of 

 magnesia 27*42, sulphate of water 69*32, crystallized cane-sugar 

 26'74', starch-sugar 26*94, gum-arabic 13*24, albumen 3*03. The 

 low diffusibility of albumen is very remarkable, and the value of this 

 property in retaining the serous fluids within the blood-vessels at 

 once suggests itself. It was further observed, that common salt, 

 sugar and urea, added to the albumen under difl'usion, diffused away 

 from the latter as readily as from their aqueous solutions. Urea 

 itself is as highly diffusible as chloride of sodium. 



In comparing the diffusion of salts dissolved in 10 times their 

 weight of water, it was found that isomorphous compounds generally 

 had an equal diffusibility, chloride of potassium corresponding with 

 chloride of ammonium, nitrate of potash with nitrate of ammonia, 

 and sulphate of magnesia with sulphate of zinc. The most remark- 

 able circumstance is that these pairs are " equi-diffusive," not for 

 chemically equivalent quantities, but for equal weights simply. The 

 acids differed greatly in diffusibility, nitric acid being nearly four 

 times more diffusive than phosphoric acid ; but these substances 

 also fell into groups, nitric and hydrochloric acids appearing to be 

 equally diffusive ; so also acetic and sulphuric acids. Soluble sub- 

 salts and the ammoniated salts of the metals present a surprisingly 

 low diffusibility ; the quantities diffused in similar circumstances 

 of the three salts, sulphate of ammonia, sulphate of copper, and the 

 blue ammonio-sulphate of copper being very nearly as 8, 4 and 1. 



When two salts are mixed in the solution-cell, they diffuse out 

 into the water atmosphere separately and independently of each 

 other, according to their individual diffusibilities. This is quite ana- 

 logous to what happens when mixed gases are diffused into air. An 

 important consequence is, that in liquid diffusion we have a new 

 method of separation or analysis for many soluble bodies, quite ana- 

 logous in principle to the separation of unequally volatile substances 

 in the process of distillation. Thus, it was shown that chlorides 

 diff'use out from sulphates and carbonates, and salts of potash from 

 salts of soda; and that from sea-water the salts of soda diffuse out 

 into pure water faster than the salts of magnesia. The latter cir- 

 cumstance was applied to explain the discordant results which have 

 been obtained by different chemists in the analyses of the water of 

 the Dead Sea, taken near the surface ; the different salts diffusing 

 up into the sheet of fresh water, with which the lake is periodically 

 covered, with unequal velocity. 



It was further shown that chemical decompositions may be pro- 



