130 Mr. S. U. Pickering on the Di fusion 



Table I., the supplementary freezing-points necessary for the 

 calculation of the strengths of the final solutions being given 

 in Table II. (In the case of cane-sugar and acetic acid the 

 determinations used for this purpose have already been 

 published, Bericlde d. deutsch. chem. Gesell. xxiv. p. 3329.) 



The values in the table refer to the weight of anhydrous 

 substance, the water of crystallization, whenever present, 

 having been allowed for. This water, in the case of alloxan, 

 was found to be 3H 2 ; whereas in the cases of gallic acid, 

 tannin, and rafhnose, 1, 2, and 5H 2 were taken as being 

 respectively present. The proportional decrease of freezing- 

 point or strength of the solution is the fraction which the 

 actual decrease is of the mean freezing-point or strength. 

 The molecular weight w! is deduced from the freezing-points 

 in accordance with van't HofF's formula 



, mean strength x 18*9 

 mean r.-p. 



The values, it will be seen, agree fairly well in most cases 

 with the theoretical molecular weights. 



The sugars as well as the tannin and dextrin were ob- 

 tained from Messrs. Trommsdorf. The dextrin, however, was 

 doubtless very far from being pure (indeed pure dextrin 

 has never yet been obtained), and very little weight can 

 be attached to the results obtained with it. The sample 

 of amylodextrin I owe to the courtesy of Mr. Horace 

 Brown : unfortunately, however, the solution used deposited 

 some of the substance during the experiments in the insoluble 

 form, and hence the results with it are very doubtful; for not 

 only is the mean strength of the solution uncertain, but the 

 amount which had diffused out is also uncertain ; for this had 

 to be estimated in the diffusate, a large quantity of it being- 

 evaporated to a small bulk so as to obtain a depression of 

 freezing-point sufficient for measurement : while, to correct 

 for solids dissolved from the dish by the liquid during its 

 evaporation, a similar volume of water was evaporated in the 

 same manner. The calculated molecular weight of the amylo- 

 dextrin was obtained from the freezing-point of the initial 

 solution, and of that entered in Table \l. The values which 

 these gave were 2519*4 and 2452*8 respectively. The results 

 with gallic acid are equally uncertain for a similar reason, the 

 solution taken having been too strong, and having deposited 

 crystals during the course of the experiment. 



In the case of pyrogallol the liquid used to make the solu- 





