JACQUES LOEB 99 



IV. Combining Ratios of Acids and Bases with Gelatin and the Viscosity 



of Gelatin Salts. 



Since Pauli's ion series was based primarily on the influence of 

 acids or their anions on the viscosity of protein solutions it seemed 

 necessary to find out whether or not viscosity measurements confirm 

 the conclusions at which we arrived on the basis of osmotic pressure 

 experiments on gelatin and egg albumin. A few remarks concerning 

 our method are required. 



The gelatin is first rendered isoelectric in the following way. 

 25 gm. of powdered gelatin of pH about 7.0 are put into 1 liter of 

 m/128 acetic acid for 30 minutes at 10°C,, after which time the acetic 

 acid is renewed and left in contact with gelatin again for 30 minutes 

 at 10°C. The acid is then decanted and replaced with distilled water 

 of about 5°C. The mixture is filtered in a Buchner funnel through 

 muslin, employing slight suction. The gelatin is then washed about 

 six times with 100 cc. of distilled water of 5° each, and is made into a 

 5 per cent solution which serves as a stock solution. The pH of 

 this solution is about 4.7, or, in other words, the gelatin is isoelectric. 



Some of the stock solution is heated to 45° and made up to a 2 per 

 cent solution in quantity sufficient for a day's experiments. This 2 

 per cent solution is kept during the day at 24°C. To 50 cc. of this 

 solution is added the desired acid or alkali in sufficient quantity and 

 then the volume is raised to 100 cc. by the addition of enough distilled 

 water. This 1 per cent solution is then rapidly brought to a tempera- 

 ture of 45°, kept there for 1 minute, and is then rapidly cooled to 24°. 

 The solution is stirred constantly during the heating and cooling. 

 The viscosity is measured immediately after the solution is cooled to 

 24°C. The measurements were all made at 24°C. by using the time 

 of outflow through a viscometer. The time of outflow of distilled 

 water through an Ostwald viscometer at 24°C. was exactly 1 minute. 

 Each measurement of viscosity was repeated with the same gelatin 

 solution and the beginning and the end of a series consisted in the 

 measurement of viscosity of isoelectric gelatin. These latter meas- 

 urements agreed in all experiments within 1 second varying only 

 between 80 and 81 seconds, thus guaranteeing the reproducible char- 

 acter of the experiments. 



