180 BIO-CHEMICAL JOURNAL 



that, as the asymptote is approached, a less and less percentage ot 

 these constituents will be taken away by repeated changes of the 

 extracting solvent. 



In order to test this hypothesis, I have taken commercial gelatin 

 and extracted it with repeated changes of distilled water at room tem- 

 perature. The comparative amounts of electrolyte removed by each 

 change were estimated by taking the electrical conductivity. Gelatin 

 at room temperature not being dissolved by water this latter can be 

 poured off and replaced by fresh with ease. Of course, the water 

 imbibed by the gelatin in swelling cannot be changed ; this does not 

 affect the result to any serious degree, merely making the process of 

 extraction a more prolonged one. The experiment was performed as 

 follows : 10 grams of Coignct's gold-label gelatin were allowed to 

 soak in distilled water until swollen and sufficient water added to 

 enable 100 c.c. to be poured off. About 180 c.c. were, needed in all. 

 A little toluol was added, and the mixture left to stand for twenty- 

 four hours. The water was then poured off and its conductivity 

 determined. A fresh 100 c.c. of water were then added, and 

 the process repeated every twenty-four hours. After the first 

 three or four extractions the conductivity of the extract was so 

 low that I found, with the apparatus used, that more accurate readings 

 were obtained by concentrating the fluid in a platinum capsule over 

 the water-bath to a definite volume (12 c.c.) before measuring its con- 

 ductivity. Even when their concentration is thus increased, the 

 electrolytes may be looked upon as practically completely dissociated, 

 so that no appreciable error can be put down to this circumstance. 

 It might be objected that impurities in the distilled water would 

 also be concentrated, but I found on testing this possibility that the 

 conductivity of the distilled water used, which had originally a 

 conductivity of 5 gemmhos ( = reciprocal megohms) did not increase 

 by concentrating 90 c.c. down to 12 c.c. Presumably, this is to be 

 accounted for by the fact that the slight conductivity was almost 

 entirely caused by carbon dioxide, which would be driven off on 

 heating. The numbers obtained were as follows : 



