64 THE GENERAL CHARACTERS OF THE PROTEINS 



iodide, 5 grams potassium iodate, and 4 c.c. concentrated sulphuric 

 acid for four hours on a water-bath. A brown precipitate was thereby 

 obtained, which was dissolved in ammonia and precipitated from this 

 solution by acetic acid ; this solution and precipitation was repeated 

 several times, and a product was obtained, which, after washing with 

 potassium iodide and then water, was found to contain 8*93 per cent, 

 of iodine. 



Kurajeff carried out a series of experiments under varying condi- 

 tions. The treatment with iodine was carried out at 40, both in acid 

 solutions and in the presence of magnesium carbonate ; he used as 

 source of iodine in some experiments, potassium iodide and iodate 

 in the presence of acids, in others iodine dissolved in potassium 

 iodide, with small quantities of iodate. When crystallised serum- 

 albumin was treated with these varying mixtures at 40-50 for from 

 three to seven days, preparations were obtained containing from 

 about 10-12 per cent, of iodine. By means of varying mixtures at 

 1 00 (one to six hours), preparations containing between 11*48 and 

 1 2'28 per cent, of iodine were obtained. 



Hofmeister's method appears to give more constant results. 

 With egg-albumin (crystallised) at the lower temperature, with 

 iodine, potassium iodide and potassium iodate, preparations con- 

 taining from 8*29-8 '42 per cent, iodine were obtained. When, 

 however, potassium iodide, with iodic and sulphuric acids, was used 

 (five days at 40 C), a preparation containing only 5*94 per cent, of 

 iodine was obtained. It may be recalled that Hofmeister's preparation , 

 obtained by treatment with potassium iodide and iodic and sulphuric 

 acid for four hours at 90-100, contained 8*93 per cent, iodine. 



Blum and Vaubel claim to be able to obtain products with con- 

 stant iodine content by their method already referred to ; they 

 propose to designate this the Blum- Vaubel iodine number, and to 

 make the preparation under the following conditions : The protein 

 is either dissolved or suspended in water, to which sodium bicar- 

 bonate is added, and the mixture is then warmed to 40-50 C. 

 Iodine dissolved in potassium iodide solution is then added in small 

 quantities at a time, till the iodine colour becomes permanent '(i.e., 

 does not disappear after half an hour) . The mixture is then cooled 

 and filtered, sodium hydroxide is added in excess, and immediately 

 afterwards acetic acid. If necessary alcohol or acetone is added 

 to complete the precipitation. The precipitate is purified by reso- 

 lution in alkali and reprecipitation by acid, and then washed by 

 water and alcohol until the washings are free from iodine. The per- 

 centage of iodine contained in the dried preparation is the ' iodine 

 number " of the protein. The iodine numbers found for various pro- 

 teins by Blum and Vaubel are as follows : Serum -globulin, 8*45 5 

 serum-albumin (preparations by different methods), 11*02 and 9*93 ; 

 " muscle-albumin," 10*37 ; egg-albumin, 7-1. 



The above examples show sufficiently the variations in the iodine 

 content of preparations prepared by different methods. 



Properties of the Halogen Derivatives of the Proteins and Nature of 

 the Action of the Halogens. 



The properties of the halogen derivatives have been to a great 

 .extent indicated. They are readily soluble in alkaline solutions, 



