.JACQUES LOEB 257 



Near pH = 7.0 the curves run parallel to the axis of absciss£e for the 

 reason that a considerable variation in pH signifies only a negligible 

 change in the concentration of gelatin salt formed. The experiments 

 were not carried beyond a pH of 12.0 on account of the lack of reli- 

 able indicators for that region, and on account of the fact that 

 alkali causes chemical changes in the gelatin. 



It should be pointed out that the maximal swelling of gelatin in 

 alkalies was less than that in acids. This was not observed in the 

 osmotic pressure curves. 



//. Relative Solubility of Different Gelatin Salts in Mixtures of Water 



and Alcohol. 



When powdered gelatin is brought to the isoelectric point, melted, 

 and made into a 1 per cent solution it is at first transparent. After 

 some time, which is the shorter the lower the temperature, the gelatin 

 solution becomes opaque; and in the course of weeks or months it 

 may settle in the form of a precipitate. This, however, does not 

 happen in each case, possibly for the reason that the precipitation will 

 occur only at a very definite pH, while, with a sHght deviation from 

 this point in either direction, the result will be only an opacity at room 

 temperature. Raising of the temperature will again result in the 

 clearing of the opacity. The opacity seems therefore to be due to 

 the formation of larger aggregates of protein molecules and these will 

 float as long as they are not too large. The setting of the solution to 

 a gel is a different process from this precipitation since no cloudiness 

 or opacity needs to be connected with this latter phenomenon. 



When we add to a freshly prepared solution of isoelectric gelatin only 

 a trace of 95 per cent alcohol the cloudiness which would have formed 

 slowly is noticed at once and if we add a little more alcohol we can 

 produce at once a dense precipitate. In order to standardize the 

 degree of cloudiness produced we add so much 95 per cent alcohol to 

 10 cc. of a 1 per cent solution of isoelectric gelatin in a test-tube of 

 definite diameter until certain letters become illegible when looked 

 at through the test-tube filled with the gelatin-alcohol-water mixture. 

 Since the addition of alcohol to the watery solution raises the tem- 

 perature and since this has the tendency to diminish the degree of 



