CORRECTNESS OF THE CHEMICAL VIEWPOINT 35 



writer's work isoelectric protein was always used as the starting 

 point for experiments. 



The procedure for preparing isoelectric protein is simple 

 enough. It is only necessary to determine the pH of a given 

 protein solution potentiometrically, and then to add very gradu- 

 ally as much acid or alkali as is required to bring it to the iso- 

 electric point. 



The following method was used to prepare larger quantities 

 of approximately isoelectric gelatin: 50 gm. of commercial 

 powdered Cooper's gelatin, which happened to have a pH of 

 6.0 to 7.0, were put into 3,000 c.c. of M/128 acetic acid in ajar 

 at 10C., and stirred frequently. After 30 minutes the super- 

 natant liquid was decanted and fresh M/128 acetic acid at 10C. 

 was added to equal the original volume. The mass was fre- 

 quently stirred, and after 30 minutes the acid was again decanted 

 and replaced by an equal volume of distilled water at 5C. The 

 gelatin was well stirred and then filtered by suction through 

 towel cloth in a Buchner funnel. It was then washed in the 

 funnel five times each with 1,000 c.c. of H 2 O at 5C. After all 

 the water was drained off, the gelatin was transferred from the 

 Buchner funnel into a large beaker which was then heated in a 

 water bath to about 50C. till the gelatin was melted. The 

 concentration of the gelatin was determined by evaporating 

 to dryness, using 10 c.c. of the melted gelatin in an electric oven 

 at 90 to 100C. for 24 hours. 



One hundred cubic centimeters of a 1 per cent gelatin solution 

 prepared in this way had no more than 1 mgm. of ash appar- 

 ently Ca 3 (PO 4 )2, i-e.. the salt contained in the solution was 

 M/30,000. Salt in this concentration does not affect the physical 

 properties of proteins, such as osmotic pressure, viscosity, P.D., 

 swelling or precipitability as will be shown in this volume. The 

 following is a result of an ash determination made by Dr. D. I. 

 Hitchcock on a sample of gelatin selected at random. The stock 

 solution contained 12.69 per cent gelatin. 



SAMPLE No. 1 SAMPLE No. 2 



Volume of solution 20 c.c. 10 c.c. 



Weight of dry gelatin 2.535 gm. 1.269 gm. 



Weight of ash 0.0024 gm. 0.0012 gm. 



Obtained qualitative tests for Fe +4+ , "Ca^, and PO^, negative tests for 

 Cl- and SOr. 



