420 



plaster of Paris, and the Hehner formula wtiere they are determined 

 by the Adams iiicth(jd, using fat-free paper. Oat of 02S analyses in 

 1887 of whole milk and skim milk, in which the fat varied from ().l to 

 10 per cent, the percentage of fat as calculated differed from the per- 

 centage of fat found by analysis by from —0.2 to +0.2 per cent, the 

 average difterence being +0.02 i)er cent. The results of more recent 

 comparisons are given in the following table: 



Comparison of percentage of fat in milk found by analysis and by calculation. 



Tear. 



I Number of 

 samples. 



1888 I 



1889 .• ^ 



1890-91 i 



73 

 143 



^5 

 119 

 143 

 207 



Description. 



Milk 



Skim milk.. 



Milk 



Skim milk. . 



MUk 



SkiiD milk.. 



—0. 2 to +0. 2 



-0. 

 -0.2 

 -0. 2 

 -0.4 

 -0.3 



+0.2 

 -fO. 2 

 -hO.2 

 +0.1 

 +Q.I 



+0.001 

 +0.019 

 —0.00 1 

 +0. 057 

 —0.143 

 —0.048 



Tlic aiitlioi iK'licvrs the larger average difference obtained in 1S!»(»-01 

 to be due to a change in the method of analysis — drying 5 grams of 

 milk on plaster of Paris instead of 10 grams, as had previously been 

 used. Differences due to this change have been repeatedly observed 

 by liim in both the i)Iasf('r and iiajxT inctliods. but he is unable to offer 

 any explanation for the difference, romitarisons of the results o])tained 

 l)y the Adams method, using fat-free paper, and l>y calculation ]»y 

 means of llehner's foiinula, show that the average difference in the 

 case of 21 samples of whole milk was +0.03, ami in the ca.se of 70 

 samples of skim milk. »>.fl per cent of fat. 



In regard to the manner iind extent of the absorption of the milk by 

 the blotting pai»er in the Adams methoil. Dr. Veith oilers the following 

 explanation : 



.Milk .sfiiiiii, i. ('. milk iniiuia fat. must not 1h< considfrcfl .1 simplo solution of 

 vjuioiis iHxlits in watt-r. Part of tin- salts, tin- milk sn^ar. and part of the jtrott-ids 

 arc certainly dissolved in the water in the nsnal .si-nse of the term, bnt far the j^reater 

 part of the jiroteids — the easeiii — in eoiineetion with the rest of the niiiural mattt-r, 

 is present in a kind of swollen state, resemldin;; Itnt not identital with solution. 

 * * * In the ])aper proicss the watery solution sinks into the hloftin;^ paper, and 

 the easein eiieasinji the fat is left on and m-ar the snrfaee. .\< lordini; to this tln'ory 

 the fat is left in contar-t with only aliont one thinl of the non-fatty solids, while 

 altont two thinls, ine]ndin<{ the whole of the milk snjjar. are removed from it. That 

 nnder sneli conditions extraction of the fat is made e.isier, ran be readily imaj^ined. 



H(^garding the n>lative propoifi<ni of the constif uents of milk solitls, 

 it is stated that ''speaking as corrci'tly as the case admits, normal milk 

 contains ash, ]>roteids. and milk sugar in the iiroportion of 2:0:1.'?." 



Determination of fat in sour milk, M. Ekenberg {('Ik in. Z///., 7.7, 

 ;). IlKi!)). — To make the milk homogeneous, so that an average sample 

 may be taken, it is lecommeiided to add ."» per cent by volume of com- 

 mercial ammonia, and shake. The milk is i<'ndered thin, and, as 

 microscopic examinations imlicatcd, perfectly homogeneous. JScveial 



