FOODS 79 



strong sulphuric and 5 grm. pot. sulphate. Heat gently 

 over a Bunsen flame until all frothing ceases, and then 

 place on a stand over a small Bunsen flame until the liquid 

 is colourless and quite clear. Cool the flask and contents, 

 and add 50 c.c. of water, and neutralize with strong NaOH 

 solution, adding slight excess to make alkaline. Distil 

 over the ammonia into 20 c.c. of normal acid sulphuric, the 

 distillation taking about an hour. Titrate with decinormal 

 alkali, using methyl orange as indicator, and the difference 

 in the titre found and what the titre should be represents 

 the amount of nitrogen in the amount of milk taken, and 

 this is converted into albuminoids by multiplying by 6-39. 



Microscopic Examination. This is always advisable. 

 The strictly normal constituents are round oil globules of 

 various sizes in an envelope and a little epithelium. The 

 abnormal constituents are epithelium in large amount, pus, 

 conglomerate masses, and casts of the lacteal tubules. The 

 added matters may be starch grains, portions of seeds, and 

 chalk. 



Bacteriological Examination. See Bacteriology. 



Proteids in Milk. Ritthausen's Method. Consists in 

 precipitating with copper hydrate, which carries down the 

 fat and proteids. The precipitate is collected, dried, and 

 weighed on the filter paper. Deductions are made for the 

 amounts of fat, salts, and copper hydrate precipitate, and 

 the weight of filter paper, and the remainder is the weight 

 of proteids in the quantity of milk taken. 



Boiled Milk. To 10 c.c. of milk sample add 1 c.c. of 

 solution of ortol and a few drops of peroxide of hydro- 

 gen solution. In unheated milk a crushed-strawberry 

 colour is produced. If the milk has been heated above 

 72 C. (i8i-6 F.) no colour will be produced, but on the 

 addition of a little unheated milk the colour will appear. 

 As milk is pasteurized at 159 F., such milk will be positive 

 to this test. Paraphenylenediamine (replacing ortol) gives 

 an indigo-violet in milk not heated above 78 C. 



Preservatives in Milk. L.G.B. Circular, 1906. " The 

 presence in milk of formalin to an amount which is ascer- 

 tained by examination within three days of collecting the 

 sample to exceed 1 part in 40,000 (1 part per 100,000 of 

 formic aldehyde) raises a strong presumption that the 



