ESTIJIATION OF TOTAL PROTEINS. 127 



crucible. The precipitate is wasted several times by decantation, 

 and then transferred to the filter or crucible, the portions adhering 

 to the beaker being removed by a " policeman." It is washed 

 a few more times with water, and the filter or crucible allowed to 

 drain. 



The filter or crucible is washed once with strong alcohol, and 

 then several times with ether, preferably in a Soxhlet extractor ; 

 it is then washed again with strong alcohol from a small wash 

 bottle, using the jet to distribute the precipitate over the 

 filter. 



The filter or crucible and its contents and the tare or the 

 crucible are dried in an air oven at a temperature of 130° C. 

 and weighed ; the filter or crucible and precipitate are inciner- 

 ated in a porcelain capsule in a muffle, going up to as high a 

 temperature as possible. The weight of the residue, minus that 

 of the ash of the filter, is subtracted from the weight of the 

 dried precipitate, the difference being the proteins. 



The author and Boseley have obtained good results by neutral- 

 ising the milk, using phenolphthalein as indicator, previous to 

 the addition of the copper sulphate solution ; the quantity of 

 the latter may also be reduced to 2'5 c.c. 



This method gives good results with all milk products, except 

 whey ; this is due to the fact that the copper salts of proteoses 

 are not insoluble in water. There is a slight tendency for the 

 results to be high, owing to copper hydroxide, which is always 

 co-precipitated, not being entirely dehydrated at 130° ; there is 

 also a tendency to be low, because the phosphorus of the casein 

 is converted into phosphoric acid on ignition, which swells the 

 amount of ash. These two errors usually compensate each other 

 to a greater or less extent. 



The washing with alcohol and ether may be omitted, and the 

 precipitate weighed as proteins and fat, the fat, estimated by 

 other methods, being subtracted from the weight. 



Bordas and Toutplain estimate proteins in milk by treating 

 10 c.c. with 20 c.c. of acetone, shaking the mixture to efiect 

 complete precipitation, and separating the precipitate in a 

 centrifuge ; the insoluble proteins are collected, washed with 

 dilute and finally with pure acetone, dried, weighed, ignited, 

 and the amount of ash deducted. 



Volumetrio Determination of the Proteins in Milk. — 

 Deniges has worked out a process which depends on the estima- 

 tion of the amount of mercury necessary to combine mth the 

 proteins ; it is worked as foUows : — 



Tweiitv-five c.c. of the milk are mixed with 5 c.c. of a saturated 



N . . 



solution of ammonium oxalate, 20 c.c. of j^ mercuric potassium 



