ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 115 
CHEESE, 
Cheese is obtained-by the rennet curdling of milk. The curd is 
cut up small and the whey expressed from it; the mass is then 
salted and allowed to ripen by bacterial and enzymic action. There 
are many kinds of cheeses, but for the purpose of this paper their 
description is unnecessary. Very little indeed is known of the 
colloid chemistry of cheese, except that portion relating to the 
action of rennet on milk and the subsequent production of curd. 
The following are some typical analyses of hard cheeses :— 
H,0. Fat. Protein. Ash. 
Per cent. Per cent. Per cent. Per cent. 
(a) Stilton..., 20°30 44-00 oat) PE 
(b) Cheshire 34°70 33°3U 26°10 4°30 
(¢) Cheddar 33°90 29:00 pei (Grey 4:05 ° 
The structure of cheese varies from a dough-like to a granular 
texture, and it is in this connection that the only colloid researches 
have been made on cheese. 
Van Dam investigated the swelling of casein under the influence 
of common salt and lactic acid. He ascertained the solubility of 
casein in solutions of NaCl (5, 3, and 1 per cent.) containing lactic 
acid, and obtained curves showing the relation between the dissolved 
casein and the concentration of the hydrogen ions. Cf. van Dam, 
Gedenkboek. aan J. M. van Bemmetn (1910), pp. 102-107. 
Chick and Martin published results on the viscosity of casein 
sols, which bear somewhat on this problem. In the case of both 
alkaline and acid casein solutions, the viscosity increases with the 
quantity of alkali or acid present, which indicates that the casein- 
salt particles have a greater adsorptive power for water than has 
casein itself. Cf. Z. Chem. Ind. Koll. 11, 102-105 (1912). 
The most important contribution to the subject, however, has 
been made by Allemann and Schmid (Landw. Jahrb. Schweiz. 30, 
357 -383 (1916) ). They investigated ‘the elasticity of the coagulum 
produced in milk by rennet.’ 
An apparatus was employed which measured the resistance 
‘which the curd offered to a vertical rod carrying three concentric 
rings. Thus they were able to investigate the effect of time, con- 
- centration of rennet, concentration of acid, and other factors, on the 
curd produced. It was found that the elasticity of the curd 
increased in direct proportion to (a) acidity of milk, (¥) concentra- 
tion of the rennet, (c¢) addition of soluble calcium salts, (¢) rise in 
temperature. No apparent maximum of elasticity was ascertained 
with ascending temperatures, though the time required for coagula- 
tion‘ reached a maximum at 41° C. Agitation during curdling 
inhibits the velocity about 8 per cent. With cold milk, a longer 
time was required for curdling, and the resulting curd had a 
decreased elasticity. 
The whole question of the structure of cheese still remains open 
for research, as also does the question as to the physical state of the 
fat globules present. See Stocking, ‘Manual of Milk Products’, 
_ chap. 9 (1917), 
