LACTALBUMIN. 61 



Lactalbumin, like other albumins, is not precipitated by 

 saturating its solution with magnesium sulphate ; but on the 

 addition of acetic acid to the solution a precipitate of albumin is 

 obtained, and this is redissolved on neutralisation of the acid. 

 It can be obtained in a crystalline form by diluting the saturated 

 magnesium sulphate solution with an equal bulk of water, adding 

 acetic acid till permanently turbid, and setting aside. Gentle 

 shaking assists the crystallisation. It is, like other albumins, 

 precipitated by sodium sulphate added to saturation, and also 

 by ammonium sulphate. It is also precipitated by tannin, 

 phospho-tungstic acid, and other general reagents. The salts of 

 albumin with copper, mercury, and lead are insoluble. Alcohol 

 precipitates it and the precipitated albumin is soluble in water. 

 It has a specific rotatory power [ct] D of 67-5 (Bechamp). 



Lactalbumin has the following composition, according to 

 Sebelein : 



Per cent. 



Carbon, - - - 52 '19 

 Hydrogen, - - 7 '18 

 Nitrogen, - - 15 '7 7 



Per cent. 



Sulphur, - - 1-73 



Oxygen, - - 23 '13 



It differs from casein by containing no phosphorus and about 

 twice as much sulphur. When boiled with an alkaline solution 

 of lead acetate it gives a very strong sulphur reaction. There 

 appears to be no difference in elementary composition between 

 soluble and coagulated albumin. Abderhalden and Hunter state 

 that the mixed coagulable proteins of milk contain 1-2 per cent, 

 of glycine. 



Preparation of Lactalbumin. Milk is saturated with 

 magnesium sulphate and filtered. To the clear filtrate is added 

 as much acetic acid as will give per cent, of acetic acid ; lact- 

 albumin is precipitated, and is filtered off. The precipitate, 

 with the filter, is stirred up with water, and the acid neutral- 

 ised ; the lactalbumin dissolves. The solution is filtered, and 

 reprecipitated by saturating with magnesium sulphate and 

 adding J per cent, of acetic acid ; this is repeated three or four 

 times ; the solution of lactalbumin is then dialysed to remove 

 salts. The solution is precipitated by alcohol, the precipitate 

 washed with alcohol and ether and, finally, dried at a low tem- 

 perature. Lactalbumin, prepared in this way, is a white powder 

 without taste, and completely soluble in water. 



The albumoses are bodies analogous to the caseoses ; they are 

 not, however, precipitated by acids, and are less readily preci- 

 pitated by copper sulphate. 



Lacto-G-lobulin. This protein is coagulated by heat and 

 precipitated by neutral sulphates, tannin, etc. ; rennet does not 

 coagulate it. It coagulates at 72 C. It only occurs in traces 



