 ————ree 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 107 
solution by boiling with alkali, or salts which react alkaline, e.., 
sodium phosphate. 
Thus, von Riegler [Fr. Pat. 461131 (1913)], prepared an artificial 
milk by dissolving gluten in caustic potash. It is usual, however, 
to emulsify a small quantity of oil (say 3 per cent.) with this colloidal 
solution of casein, and then to add small quantities of lactose, lactic 
acid, citric acid, etc., to render the similarity to milk more complete. 
Other ingredients which find their way into artificial milks are 
dextrin, malt extract, sucrose, dextrose, honey, NaCl, NaH CO,, egg 
yolk, and preservatives. 
Artificial milk can be “soured” by inoculation with lactic 
bacilli, and may be condensed, or made into artificial cream, butter, 
or cheese. Undoubtedly, a big future awaits this product, and it 
marks an especial advance in its use in margarine manufacture. 
For further details cf. :— 
Melhuish, Brit. Pat., 24572 (1913) ; Gossel, Fr. Pat., 451447 (1912), and Eng. Pat., 
27860 (1912) ; Monahan & Pope, U.S. Pat., 1104376 (1914) ; Y.Y. Li, Eng. Pat. 30275 
(1910) ; Kaufmann, Eng. Pat., 7296 (1913); Liebrich, Eng. Pat., 12355 (1898) ; 
Melhuish, Eng. Pat., 9626 (1915) ; Beckmann « Dyck, U.S. Pat., 1216052 (1917). 
The Enzymes of Milk. 
Enzymes are colloids, constituting a special class of catalysts, the 
catalysts being living organisms. Their presence in milk gives rise 
to some interesting facts explicable along the lines of our modern 
notions concerning colloid phenomena. The following enzymes are 
present in cows’ milk :— 
(a) Peroxidase. 
(b) Reductase (indirect). 
(c) Catalase. 
(d) Amylase. 
There is no conclusive evidence of the presence of proteolytic 
enzymes, lipolytic (fat-splitting) enzymes, or of lactase. 
(a) Peroxidase. 
This enzyme is always present in cows’ milk, and its destruction 
by heat furnishes the basis of numerous tests devised to distinguish 
between pasteurised and unpasieurised milks. The first test used 
was to add tincture of guaiacum and H,0, to milk, when, if per- 
oxidase was.present, a blue colour appeared. This test depended on 
the fact that guaiaconic acid (present in guaiacum) oxidises to a blue 
compound. It is noteworthy that HO. alone does not give this 
coloration with guaiaconic acid; an activator must be present to 
give the activating impulse to H2O2 and then oxidation can take 
place. Such an activator is peroxidase the enzyme of oxidation. The 
active system, peroxide plus peroxidase, is termed an * oxidase.” 
The enzyme is destroyed by heat; also it behaves catalytically, 
since extremely large amounts of peroxides can be acted upon, 
provided an oxidisable body be present. 
The guaiacum test is replaced to a large extent by Storch’s more 
reliable test involving the use of para-phenylene-diamine, and H,O.. 
