14 PROTEIDS. 



rated at 30 with magnesium sulphate and the precipitated globulin 1 is 

 washed on the filter with a saturated solution of the salt. The filtrates 

 are then saturated at 40 with sodium sulphate; by this means the 

 serum-albumin is precipitated. The precipitate is dissolved in water, 

 reprecipitated by sodium sulphate, and the process repeated several 

 times. The final product is then freed from salts by dialysis, pre- 

 cipitated by excess of alcohol, washed with this and finally with ether 

 and dried by exposure to the air 2 . 



The facts on which this method is based were clearly stated by Denis 3 . Schafer 

 rediscovered 4 the precipitability of serum-albumin by sodium sulphate in presence 

 of the magnesium salt. Halliburton has shewn 5 that this is due to the action of the 

 double sulphate of magnesium and sodium Mg Na 2 (S0 4 ) 2 6H 2 0. 



CLASS II. Derived Albumins (Albuminates) 

 1. Acid-albumin. 



When a native albumin in solution, such as egg- or serum-albumin, 

 is treated for some little time with a dilute acid, such as hydrochloric, 

 its properties become entirely changed. The most marked changes are 

 (1) that the solution is no longer coagulated by heat ; (2) that when the 

 solution is carefully neutralized the whole of the proteid is thrown down 

 as a precipitate ; in other words, the serum-albumin, which was soluble 

 in water, or at least in a neutral fluid containing only a small quantity 

 of neutral salts, has become converted into a substance insoluble in water 

 or in similar neutral fluids. The body into which serum-albumin thus 

 becomes converted by the action of an acid is spoken of as acid-albumin. 

 Its characteristic features are that it is insoluble in distilled water, and 

 in neutral saline solutions, such as those of sodic chloride, that it is 

 readily soluble in dilute acids or dilute alkalis, and that its solutions in 

 acids or alkalis are not coagulated by boiling. When suspended, in the 

 undissolved state, in water, and heated to 7'5 C., it becomes coagulated, 

 and is then undistinguishable from coagulated serum-albumin, or indeed 

 from any other form of coagulated proteid. It is evident that the sub- 

 stance when in solution in a dilute acid is in a different condition from 

 that in which it is when precipitated by neutralisation. If a quantity 

 of serum- or egg-albumin be treated with dilute hydrochloric acid, it 

 will be found that the conversion of the native albumin into acid- 

 albumin is gradual ; a specimen heated to 75 C. immediately after the 

 addition of the dilute acid, will coagulate almost as usual ; and another 



1 Hammarsten, Zt. f. phijsiol. Ch. Bd. vm. (1884), S. 467. 



2 Starke, loc. cit. (sub. egg-albumin), S. 18. 



3 Etudes sur le sang, Paris, 1859, p. 39. 



4 JL of Physiol. Vol. in. (1880), p. 184. 



5 Ibid. Vol. v. 1883, p. 181. 



