96 REPORTS ON THE STATE OF SCIENCE.—1918. 
COLLOID PROBLEMS IN DAIRY CHEMISTRY. 
(Milk, Butter, Cheese, Margarine, and Ice-cream.) 
By WI.LLiaM CLAYTON, M.Sc., Chief Chemist, Calders Margarine 
Co., Liverpool. 
In this paper it is proposed to treat of Dairy Chemistry under 
special headings, drawing particular attention to the colloid phe- 
nomena and problems involved. Milk (the basis of all the other 
products), butter, cheese, margarine, and ice-cream, each receive 
special consideration :— 
MILK. 
Milk contains substances which are inherently colloidal in nature, 
é.g., casein and albumen, and also materials which behave as colloidal 
systems by virtue of their fine state of subdivision, e.g., the fat 
present as emulsion, the cell-content of milk, and the enzymes of 
milk. 
The casein of milk, a protein combined with phosphates of the 
alkaline earths, is present to the extent of about 3 per cent., whilst 
the second protein body, albumin, is present to about 0°5 per cent. 
Casein is so important from the, standpoint of the colloid chemistry 
of milk, that a separate section of the paper has been devoted to it. 
The albumin, known as lact-albumin, is separated from casein, by 
precipitating the latter with acetic acid. Pure lact-albumin is an 
amorphous, tasteless powder. In aqueous solution it is coagulated 
by heating to 70° C., but only about 85 per cent. to 90 per cent. is thus 
precipitated. [See Rupps. U.S. Dept. Agri. Bureau of Animal, Ind, 
Bull. 166. Pp. 1-15. (April, 1913).] Lact-albumin is soluble in 
saturated aqueous Mg SOx, but is precipitated if acetic acid be added. 
A crystalline form of this albumin is obtained if the saturated Mg 
SO, solution has an equal volume of water added, a little acetic acid 
being present, and then allowed to stand. 
Amongst other reactions given by the albumin proteins,’ lact- 
albumin is thrown out of solution by saturation with ammonium 
sulphate, or by addition of tannin, or phosphotungstic acid. It is 
insoluble in alcohol. 
Some evidence has been obtained for the existence in milk of a 
third protein, lacto-globulin, present to the extent of about 0°15 per 
cent. It is soluble in acidified NaCl solutions, is coagulated at 72°C., 
is not coagulated by rennet, and is precipitated by sodium sulphate, 
and tannin. 
Hammarsten, 7. f. physiol. Chemie, &, 467 (1183-4). 
Sen Sebetien, 4. f. physiol. Chemie, 9, 445 (1885). 
Schlossmann, Z. f. physiol. Chemie, 22, 197 (1896). 
The colloid chemistry of milk chiefly centres round the phe- 
nomenon of “ protection,” in this case, the protective action exerted 
by lact-albumin on casein. The subject has been well investigated, 
and is fairly involved ; for its complete understanding, the com- 
positions of various milks ‘must be studied. The following table of 
