— 1 oe 4 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 1O1 
The elemental analysis of casein derived from Cows’ and from 
Human milk respectively are :— 
Casein. 
Cows’. Fluman. 
6 52°69 i cent. 52°24 per cent. ef. Lane — Claypon 
Se ee SNE ia Milk and its Hy- 
S 0-832 112 EE gienic Relations” 
P Os77. (ean «a | (1916), p. 37. 
di 58 
” 
_ Casein is amphoteric in reaction, though its acidic functions are 
more pronounced, when it béhaves as a tri-basic acid. When dis- 
solved in dilute alkali a /-rotatory solution ensues. 
Exactly as to how casein existsin milk is still a debatable point. 
Some authors believe it exists as a salt of lactic acid, casein-lactate. 
That lactic acid and casein do unite was shown by W. Van Dam 
(Chem. Weekbiad. 7, 1013 (1910)). This author, using Bredig’s ethyl 
diazo-acetate method, determined the reduction of the H ions in 
solutions of lactic acid produced by adding various amounts of 
casein. The casein combined with a constant amount of lactic acid, 
viz., 4°25 per cent. 
Revis and Payne infer a combination of casein with calcium 
phosphate. Richmond adduces evidence “that casein exists in milk 
as a calcium sodium salt, combined with one molecular proportion - 
tricalcium. phosphate.” (Dair y Chemistry (1914), p. 30). 
Casein is not coagulated when milk is boiled, but aivaxatiane 
occur in the molecule affecting the action thereon of digestive 
ferments, and in all probability increases the digestibility. 
At higher temperatures than boiling, casein suffers partial 
coagulation, e.g., at 130°-140° C., and Jensen and Plattner are of the 
opinion that the browning of milk so heated, is caused by the incip- 
ient breaking down of the casein.” (fev. gen. du Lait IV, 361-388 
(1904-5).) i 
Cf. Also Conradi “ Ueber den Einfluss erhéhter Temperaturen 
auf das Casein der Milch.” Miinch. med. Wochensch. 48, 175 (1901). 
The estimation of casein in milk is madeas follows :—10 grs. of 
milk are diluted to 100 cc. and warmed to 42°C. 1:5 ce. of a 10 
per cent. solution of acetic acid are added, and the mixture well 
stirred. The precipitated casein is allowed to settle for about 10 
minutes, filtered on to a tared filter paper, dried at 105° C. and 
weighed. Ignite, and subtract the ash, plus the ash of the filter 
paper, from the total weight. 
Casein is typically colloidal in nature as may be inferred from its 
behaviour in solution. It acts as a protective colloid, and stable sols 
of silver or cadmium sulphides are readily prepared by passing H.S 
threugh solutions of silver or cadmium salts containing casein. Its 
gold number (determined in solution in ammonia) is 0:01, which 
stands quite high in the list of protective colloids arranged in the 
order of their gold no., i.e., power of protection. 
Casein combines with a fixed amount of NaOH (1 gr. requiring 
0°88 millimol of NaOH) yielding a solution which has a normal 
electrical conductivity, but which does not pass through parchment 
when dialysed. 
20895 . D3 
