193 



In the cases of samples 3 and G there was little increase in fat 

 after the lirst three siphonings, occui^yiug only about 15 minutes. In 

 the opinion of the author "continuing the extraction for an hour 

 appears to be more than suflicient for all practical i)urposes." 



A comparison of methods of determiining fat in milk, L. F. 



Nilson {('Itcin. Ztij., /J, pp. iii'J-(i5ii). — The ]>ri]u;iry object of this study 

 of met hods was to test the lactocrite and Soxhlet aerometric methods 

 for the rapid determination of the fat in milk, and to compare their 

 accuracy with that of several gravimetric methods. In the course of 

 the investigation considerable information of interest was brought out 

 with regard to the gravimetric methods most generally in use, and 

 chiefly these will be considered here. 



In the tests with the lactocrite a mixture of hydrochloric and lactic 

 acids was used for dissolving the casein, instead of a mixture of sul- 

 phuric and glacial acetic acids. Of the gravimetric methods in which 

 the milk is absorbed by some porous substance and dried previous to 

 the extraction of the fat, experiments were made with the following : 



(1) Pumice stone prepared by grinding and sifting so as to secure a 

 material the particles of which were not over 1 mm. in diameter, wash- 

 ing with Avater, and igniting. To about 12 grams of this material in a 

 porcelain dish about 12 grams of milk were slowly added, and the 

 whole dried at 97-98° C, the drying being hastened toward the end by 

 placing in an air-tight oven partially exhausted by a Alter pump. The 

 dried residue was collected and placed in a paper cartridge made of the 

 best Swedish tilter paper, used double, which had been previously 

 extracted with ether for at least 12 hours. A plug of cotton was i^laced 

 in the bottom of the cartridge and another in the bottom of the 

 extractor to retain the liner particles of pumice. A Soxhlet extraction 

 apparatus and ether free from alcohol and water were used for the 

 extraction. The objection found to ])umice stone as an absorbent was 

 that its pores are too large and do not enable a sufficiently line 

 distribution of the particles of inilk solids. The fat globules remain to 

 some extent inclosed in casein, so that a pulverizing of the dried material 

 before extraction becomes essential to accurate results. This method 

 was discarded after a few tests. 



(2) The next material used to absorb the milk was unglazed, lightly 

 burnt earthenware, which was reduced to about the same fineness as 

 the pumice stone and washed on a sieve. This was used in the same 

 manner as the pumice stone, except that about 22 grams of the absorb- 

 ent were used with 10 grams of milk. Tests were made with whole and 

 skim milk as to the time necessary to complete the extraction of the fat. 

 The use of the double paper cartridge and the cotton made the percola- 

 tion of the ether somewhat slow and thus lengthened the time necessary 

 for the extraction. It was found that from 3 to 5 hours were sufficient 

 for whole milk, but in the case of skim milk containing 0.85 per cent of 

 fat 5 hours seemed not to be sufficient. 



