Tlte Viscosity of Cream. 319 



tlie samples of cream employed, it is reasonable to assume that any 

 increase in the viscosity of separated milk corresponding to that 

 at the critical acidity of cream scrum could have been detected Ijy 

 the use of the smaller capillary, and as no such rise is discernible, 

 the critical acidity must be due to the change in the nature of the 

 envelopes of the fat globules, and not to the addition to the li(|uid 

 of solid maltei- in the form of i)recipitate. 



I/iflut/ire of Tenipe rat lire on Crciii/i V/scostfi/. 



The effect of rise of temperature of the cream is, as one would 

 naturally expect from the case of other tiuids, to diminish the 

 viscosity, at first rapidly, but after reaching a temperature of 

 about 35 deg. C, the decrease in viscosity due to a further increase 

 in temperature is less marked. At about this temperature the fat 

 conunences to melt, and the globules tend to coalesce, so that the 

 nature of the liquid is changed, and the results of further rise of 

 temperature are no longer comparable with those obtained by ex- 

 periment with liquids containing suspended particles which are 

 not thus affected by change of temperature. 



F(tt Content as Affecting Viscosity. 



For the investigation of the effect of the fat content of cream 

 in determining its viscosity, a number of sam2:)les of cream, separ- 

 ated from the same milk, and differing only in fat content, were 

 employed, the experiments being performed, as before, at a con- 

 stant temperature of 25 deg. C, with an Ostwald viscosimeter. 



The residts of these experiments show that the viscosity of cream 

 increases with increase in the fat conent, at first slowly, then more 

 and more rapidly, till a viscosity is attained such that the cream 

 will no longer flow. 



In an interesting paper by Walter Hess, in Pflliger's Archiv. fiir 

 Physiologic, May, 1911, on " Blutviskositat unci Blutkorperchen," 

 a new theory of the relation betAveen viscosity and content of solid 

 particles in blood was put forward. It is as follows : — Supposing 

 a number of samples of blood, the plasma of Avhich has the same 

 viscosity for all, but which contain different (juantities of solid par- 

 ticles, amounting to 10 per cent., 20 per cent., and 30 per cent., 

 and so on for the different samples, the viscosity of any sample 

 will be inversely proportional to the amount of plasma contained. 



Hence the viscosities of the various samples will be 100/90, 

 100/80, 100/70. etc., of the viscosity of the plasma, and hence the 



