18 MILK 
materials may be removed from the tube, and, 
replacing the parts of the apparatus, much of 
the solvent may be redistilled into the extractor, 
thus recovering the liquid. Care must be taken 
not to distil the contents of the flask closely or 
heat strongly, lest some of the more volatile of 
the dissolved matters pass into the distillate. 
Roese-Gotilieb Method.—This is now being used 
for milk-products as well as for milk. For de- 
tailed description, see page 72. 
Centrifugal Methods.—Although almost all the 
fat of milk may be separated by the centrifuge, 
the emulsion is not destroyed and the volume of 
cream is merely suggestive as to the fat-content 
of the milk. To obtain a clear fatty layer in 
condition for close measurement it is necessary 
to use chemicals. The methods at present most 
employed depend essentially on one devised by 
Gustaf DeLaval, who took out a patent in Sweden 
for the use of a mixture of twenty volumes of 
strong acetic acid and one volume of strong 
sulfuric acid. This mixture coagulates and then 
dissolves the proteins, destroys the emulsion, but 
does not otherwise affect the fat and does not 
act on the lactose. By brief whirling in a cen- 
trifuge the fat collects in a clear sharply defined 
layer. DeLaval took out patents in several 
countries subsequent to the above date. 
Leffmann and Beam devised a metliod in which 
