PRESERVATION OF MILK SAMPLES. 189' 



as the control, add very carefully a ~ solution of caustic soda 



drop by drop till the correct shade is obtained. 



(4) Plug all tubes with cotton wool, and heat them in a water 

 bath kept at 80° C. for ten minutes. 



(.5) Cool the tubes, and add to each 0"-5 c.c. of a solution con- 

 taining 05 c.c. of sour milk per 100 c.c, shake well, and let the- 

 tubes stand for twenty-four hours at a temperature between 

 15' C. and 24° C, or until the control tube is white. 



If preservatives are absent the milk will become white at the 

 same time as the control ; in the presence of preservatives the 

 tubes will remain blue or pink. 



If formaldehyde is found a quantitative estimation may be 

 made by making up a series of tubes containing known amounts 

 of formaldehyde, and keeping these and the tubes of the milks 

 to hi' tested at a temperature of .37° C. ; it is also advisable to 

 dilute the milk 10 and 100 times, prepare tubes from the diluted 

 milk, and keep these at '22° C. The controls kept at 37° may 

 contain 0"005, 0"003, and O'OOl per cent, formaldehyde, and 

 those kept at 22°, Q-OOl, 0-0008, 0-0005, and 0-0003 per cent. 



By notint; which of the control tubes is decolourised at the- 

 same time as the sample to be tested, a fairly accurate estimation 

 of the amount of formaldehyde present may be made. 



Preservation of Milk Samples. 



Where any special importance is attached to the analysis oi 

 any sample, it is an advantage to preserve the sample for refer- 

 ence and further corroborative analysis, Preservatives are added 

 to effect this. The following substances have been used : — 



Alcohol. — Allen has suggested adding to the milk to be kept 

 twice its weight of alcohol ; his experience and that of Hehner 

 show that analytical data can be obtained on the preserved milk 

 (makinji allowance for the alcohol added) which agree with the 

 original sample. The objection to this method is that a large 

 amount of a volatile substance is added, and a correction, the 

 exactness of which depends on the amount of alcohol present, 

 must be made. Milk-sugar and salts are also deposited after 

 sonic time, and are difhcult of complete redistribution. 



Chloroform. — When added in the proportion of 1 c.c. to 

 100 c.c. of milk it keeps the milk well for a short time. It has 

 the advantage of dissolving in the fat and keeping the cream in 

 an easily miscible condition. As Babcock and EusseU have 

 sliown, it does not stop enzymic action ; hence changes in the 

 proteins, due to this cause, proceed as if no chloroform had beeiL 



