18 CONSTITUENTS OF MILK 



sulphate but is precipitated by the addition of small quantities 

 of acetic acid. It is stated that lactalbumin may be obtained 

 in a crystalline form by diluting the saturated magnesium sul- 

 phate solution with an equal volume of water and setting aside 

 after the addition of acetic acid until permanently turbid. 



Lactalbumin is also precipitated by sodium and ammonium 

 sulphates when added to saturation. Tannin, phosphotungstic 

 acid and other general reagents also precipitate lactalbumin: 

 the salts of the heavy metals are insoluble in water. Lactal- 

 bumin is insoluble in alcohol and this reagent may be employed 

 for the precipitation of lactalbimiin from aqueous solutions: 

 the precipitate so obtained is easily soluble in water. 



Lactalbumin is a white powder possessing neither taste nor 

 odour. It coagulates at 70** C. but the precipitation is never 

 complete. The specific rotatory power, according to B^champ, 

 is[Q:]D= — 67.5, but Sebelein obtained values varying from 

 -36.4 to -38.0. Lindet26 obtained a value of only -30.0, so 

 that apparently the preparations of both B^champ and Sebelein 

 were mixtures of lactalbumin with some other substance, prob- 

 ably caseinogen [a]/3=— 119, having a much higher rotatory 

 power. 



Lactoglobulin. Comparatively little is known regarding 

 the globulin constituent of milk. It is precipitated by neutral 

 sulphates such as magnesium sulphate but is quite soluble in 

 sodium chloride solutions even after acidification. It is not 

 clotted by rennin but coagulates under the action of heat alone 

 at a temperature of 72° C. (Hewlett). 



Probably not more than 0.1 per cent of lactoglobulin is 

 present in normal milk although considerably more may be 

 found in colostrum. 



Mucoid Proteid. This substance, according to Storch, 

 contains 14.76 per cent of nitrogen and 2.2 per cent of sulphur. 

 It is a greyish white powder which is slightly soluble in dilute 

 sodium and potassium hydrates though insoluble in ammonium 

 hydrate, acetic, and hydrochloric acids. Mucoid proteid gives 

 the usual proteid reactions with Millon's reagent (red), and 



