76 ANALYSIS OF MILK. 



change in specific gravity has been called). In about 70 per 

 cent, of his experiments the rise in specific gravity has been 

 observed, varying from 0'0015 to O'OOOS, and averaging 0'0006, 

 while in 30 per cent, of the observations no rise in specific gravity 

 was indicated. 



The experiences of Babcock and Farrington agree with that of 

 the author. 



The author's experiments have confirmed the statement of 

 Recknagel, that the rise is more rapid when the temperature is 

 low than when high ; the same ultimate specific gravity is attained 

 whatever the temperature. 



Recknagel's phenomenon appears to be unconnected with the 

 milk-sugar, and Recknagel's explanation is not the correct one. 

 It is difficult to reconcile the idea that it is enzymic, with the 

 fact that the rise is more rapid at low than high temperatures. 



The author's experiments on the change of density and specific 

 heat of cream by heating made in conjunction with S. 0. Rich- 

 mond have shown that Recknagel's phenomenon is due largely 

 to the increase of density of the fat on solidification. 



Contrary to the author's former conjecture, there seem to be 

 no particular periods of the year in which Recknagel's pheno- 

 menon is observed or not. Samples have been found at all 

 seasons which show a marked change in specific gravity, while 

 others examined almost simultaneously have shown no change. 



It must be mentioned that Recknagel's phenomenon has been 

 denied by some. Smetham attributes the change in specific 

 gravity solely to the presence of air bubbles. The weight of 

 evidence is, however, greatly against this view ; it is incon- 

 ceivable that air bubbles generated by milking a cow should be 

 persistent for twelve hours, while if they are formed in the milk 

 by other means, say by running through a separator, they dis- 

 appear in one hour. 



The final specific gravity is always taken as the true specific 

 gravity of milk, and the term is so used in this volume. 



The Estimation of Total Solids.— The total solids of milk are 

 estimated by evaporating the water and weighing the residue. 



Wanklyn's Method.— Wanklyn proposed to limit the time 

 of drying to three hours at the temperature of boiling water ; 

 he weighed 5 grammes in a platinum basin, kept it for three 

 hours on a briskly boiling water-bath, and, after cooling in a 

 desiccator, weighed the residue. This method has now entirely 

 fallen into disuse, as the residue thus obtained still contained 

 a quantity of water, which could be driven off by further 

 evaporation. 



Method of Society of Public Analysts.— A very obvious 

 modification of this is to continue the drying on a water-bath or 



