390 
heating 5 grams of the milk on the steam bath for three hours, in 
small flat platinum dishes. At the end of this time the dishes were 
removed from the steam bath and while still hot were wiped dry 
with a piece of soft toweling. They were then allowed to cool and 
weighed. In this way we obtained the weight of the residue from 
5 grams of milk, and from this we calculated the percentage of total 
solids. The ash of the milk was then determined on the same sample 
by ignition at a low red heat, cooling and weighing the dish and its 
contents the second time. The ash left after this operation was 
tested for boric acid by the turmeric test. 
Fat. — The quantity of butter fat in the milk was determined by 
the Babcock centrifugal method. This- is the most rapid method 
known for the determination of fat in milk. It compares very 
favorably with the most exact methods now known for the determi- 
nation of fat in milk, and it is the method ordinarily employed in 
practice for this purpose. 
Lactose . — The amount of lactose in the several samples of milk 
was determined polarimetrically after the removal of the milk pro- 
teids by means of an acid solution of mercuric nitrate. 
Acidity . — The acidity of the milk was determined by titrating 50 
cubic centimeters of the sample with tenth-normal sodium hydroxide, 
using phenolphthalein as the indicator. 
One cubic centiiqeter' of tenth-normal sodium hydroxide, contain- 
ing 0.004 gram of sodium hydroxide, is equivalent to 0.009 gram of 
lactic acid. Hence each cubic centimeter of tenth-normal sodium 
hydroxide required by the 50-cubic-centimeter sample of milk is equiva- 
lent to 0.018 per cent of lactic acid. In order, therefore, to obtain the 
per cent of acidity of the sample we multiply the number of cubic 
centimeters of tenth-normal sodium hydroxide required for neutrali- 
zation by 0.018. The product is the acidity of the milk in percentage 
of lactic acid. 
Thoerner (2) has suggested as a practical limit for wholesome milk 
an acidity equal to one-fifth of the volume of the milk in cubic cen- 
timeters of tenth-normal caustic soda. This would correspond to an 
acidity of 0.18 per cent of lactic acid. According to Yan Slyke (3), 
the average acidity of English market milk, supposed to be 12 to 18 
hours old, is 0.18 per cent, and of German milk 0.13 to 0.18 per cent. 
According to this author, market milk should not in any case contain 
over 0.2 per cent total acidity when it reaches the consumer, and 
generally should be under 0.15 per cent. According to Tuley (4), 
the milk of swill-fed cows is hyperacid. 
Dirt. -The quantity of dirt or suspended matter in the milk may be 
estimated either gravimetric ally (Renk, quoted by Ott (5)) or volu- 
