l66 CHEMISTR V FOR A GRICUL TURAL STUDENTS 



ness, and the residue ignited, an ash is left, consisting of the phosphates 

 and chlorides of potassium, sodium, calcium, and magnesium. 



2. Souring of Milk. — This is due to the action of the lactic ferment, a 

 micro-organism which converts milk sugar into lactic acid by hydrolysis : — 



C12H22O11 + H2O = 4C3Hg03. 



Lactic acid is able to coagulate the albuminoid of milk. Warmth aids 

 coagulation, and in hot weather it is sometimes noticed that spontaneous 

 coagulation occurs when only very small quantities of lactic acid have been 

 produced. This souring of milk is prevented by cooling the milk to near 

 the freezing point, which inhibits the action of the organisms, or by heating 

 under pressure to 120° C, a temperature which destroys the organisms, and 

 afterwards excluding air. The souring is also retarded ( i ) by heating to 

 56° C, a temperature which destroys some germs but does not affect the 

 taste of the milk, (2) by cooling even a few degrees, and (3) by the use of anti- 

 septics, such as boracic acid (H3BO3 or B2O3.3H2O from the non-metallic 

 element boron), borax {Na2B407 or 2B203.Na20), salicylic acid and formic 

 aldehyde, the addition of which are, however, considered inadmissible. ' 



3. Adtdteration. — Owing to the great variability in the composition of 

 milk due to the animal, the time of milking, the pasturage, etc., the detec- 

 tion of adulteration by water is a matter of some difficulty. The usual 

 method is to determine the specific gravity at 15.5° C. by means of the 

 hydrometer (sp. gr. = 1.028 to 1.035 for pure milk ; mean, 1.032), to weigh 

 the total solids obtained by evaporating 5 grams of milk in a weighed dish 

 on the water bath, until the weight is constant (12 to 14.5 grams per 100 

 grams of pure milk ; mean, 12.9) ; and lastly, to estimate the fat by 

 extracting it with ether or by means of a butyrometer (2.7 to 4.3 per cent.; 

 mean, 3.77). It has been found that there is a constant relation between 

 the fat and the specific gravity and total solids : —  



„ o rr, /iooS-ioo\ 

 F=.833T-2.22 y g j 



in which F = the fat, T = total solids, and S = specific gravity; hence it is 

 possible to find the amount of fat by calculation, if the specific gravity and 

 total solids are known, or the total solids by calculation if the specific 

 gravity and fat are known. 



The Chemistry of Animal and Vegetable Life. — i. Plants. — To pro- 

 mote the germination of seeds, warmth, moisture, and atmospheric oxygen 

 are necessary. The starch of the seed is converted into sugar by the diastase 

 formed during germination, and the albuminoids are converted into peptones 

 or amides ; these substances, being soluble and dialysable, can supply the 

 growing part of the plant with nutriment. The root penetrates the soil, 

 and thus procures the phosphates, sulphates, and nitrates of potassium, 

 calcium, magnesium, and iron, which the acid root sap assists in dissolving. 



