26 



genous and mineral matter. It has a slight smell and a mild, rich, 

 slightly sweetish taste. It possesses a slight amphoteric (alkaline and 

 acid ) Beaetion, due probably to the presence of alkaline carbonate and 

 neutral and acid phosphates. When allowed to stand for any length of 

 time a multitude of minute fat globules rise to the surface, and form a 

 layer of cream. By continuous standing milk coagulates. Coagulation 

 can also be brought about by the addition of small quantities of acid. 



The Ingredients of Milk. 

 The larger part of milk consists of water, which contains a variety of 

 substances in suspension and solution. The substances to a consider- 

 able extent dissolved in the water are casein and albumen, milk sugar 

 and the ashy matters. This solution forms the so-called milk serum. 

 The fat exists in the milk in suspension, in the form of very minute 

 microscopic globules. They are semi-solid and form with the serum 

 what is termed an emulsion. 



1. Milk Fab. — The fat globules in milk vary in size from .0016 of a 

 millimeter to .01 of a millimeter (555^0 ^^ tsVo of an inch), e. g., micro- 

 scopically small. The smaller the more numerous they are. As a rule 

 the globules in the milk of the Jersey and Guernsey cows are larger in 

 size than those in the milk produced by Holsteins or Ayr.^hires The 

 globules are largest in the milk of newly calved cows. The percentage 

 of fat in the milk product of the United States may be said to vary 

 between 2 25 and 8 per cent, with a probable average of 4 per cent 



Milk fat contains two kinds of fat, the so-called non-volatile and 

 volatile fats. Neutral non-volatile fat is a combination of glycerine with 

 fatty acids, such as the palmitic, stearic and oleic acids There is about 

 92 per cent of non-volatile and 8 per cent of volatile fats in the fat of 

 milk. Duclaix has estimated butter fat to be composed of the following 

 separate fats ; — 



Per Cent. 

 Palmitin, stearin, olein, with traces of myristin and butin, . 91.50 



Butyrin, 4.20 



Capronin, 2.50 



Caprylin, caprinin and traces of laui'in, 1.80 



100.00 



Butter consists largely of milk fat (85 per cent) and hence the value 

 of milk for butter depends upou the quantity of fat it contains 



2. Milk Albuminoids {Nitrogenous Matter). — The albuminoid or 

 nitrogenous portion of milk contains five distinct substances, namely, 

 casein, albumin, lactoglobulin, lactoprotein and fibrin. 



Casein forms about 80 per cent of the total albuminoids. It exists in 

 the milk, combined with lime in a semi-dissolved condition, and possesses 

 a certain amount of opacity (lack of transparency). The proportions in 

 which the casein and lime exist in combination are 100 parts of the 

 former to 1 .55 of the latter. 



Casein forms the chief constituent of the milk curd, which separates 

 out when the milk becomes sour. Casein is one of the two chief ingre- 



