CHAP. VII 



HALOGEN-ALBUMINS 



231 



at a temperature of 40-50. One portion of the iodine is substituted 

 for the hydrogen in the aromatic group as already explained, while 

 another portion is converted into hydrogen iodide, HI. To prevent 

 the latter from dissociating the albumin, Hofmeister adds magnesium 

 carbonate, MgC0 3 . Blum adds, from the very commencement, an 

 excess of sodium bicarbonate, NaHC0 3 . 



The iodo-albumins are brown loose powders, not soluble in water, 

 alcohol, or acids, but very soluble in fixed alkalies, ammonia, and 

 alkali-carbonates ; they are precipitated from their solutions by acids, 

 but pass again into solution if too much acid be added. They are 

 precipitated in the same way as are other albumins; as to colour 

 reactions they give positive results with the biuret, the xantho-proteic, 

 and Molisch's tests, but negative results with the tests of Millon and 

 Adamkiewicz, and also with the lead sulphide reaction. Apart from 

 the iodine, these proteids do not differ essentially from other albumins 

 in their percentage composition ; the sulphur content is not altered, 

 lodo-casein contains phosphorus, according to Liebrecht; the iodo-hsemo- 

 globin, according to Bohm and Berg and Hopkins and Pinkus, also iron. 



The amount of iodine contained in albumins varies. For 

 approximately pure albumins, the following numbers are given : 



Per cent. 



Serum-albumin (Kurajeff) . .12 



Serum-globulin (Hopkins) . . 13-14 



Haemoglobin (Kurajeff) . .11-12 



Egg-albumin (Hofmeister) . . 8 '9 3 



Egg-white (Blum) ' . . . 7'1 



Muscle-albumin (Blum) . . 10-11 



(Kurajeff) . .11 



Caseinogen (Blum) . . . 7-7 '5 



(Liebrecht) . . . 5 -7-8 -7 



(Oswald) . . ~ 11-13 



Gelatin (Oswald) [.'_ . . 1'3-2'0 



Thyro-globulin (Blum) . . 6-6 '6 



Nucleo-histone (Blum) . . 11-22 



The iodo- egg -albumin possesses according to Hofmeister the 

 composition : 



C H N S I 



47-92 6-6 14-27 1*26 8'93 



From this percentage composition Hofmeister calculates the 

 formula : 



^227 H 370 *4 N 48 S 2 ^75 



