80 CHEMICAL EXAMINATION 



through paper and 35 c.cms. of the filtrate, which should be 

 bright, are transferred to one of the beakers which accompany 

 the Zeiss immersion refractometer. The refraction is then 

 determined at exactly 20.0 C. A reading between 39.0 and 

 40.0 is suspicious whilst one less than 39.0 indicates the addition 

 of water. 



Lythgoe 1 after determining the value of K in the Lorenz and 

 Lorentz formula 



n 2 -l d_ K 



ft 2 +2*l~ 



which expresses the relation between the refractive index (ft) 

 and the specific gravity (d), has calculated the values of d for 

 the various scale readings of the immersion refractometer, and 

 in the absence of this instrument, the specific gravity deter- 

 mination will achieve the same object after reference to Lyth- 

 goe's table. (Table XXXV, p. 79.) 



DETECTION AND ESTIMATION OF PRESERVATIVES 



The addition of preservatives to milk is usually absolutely 

 prohibited because it has been found perfectly feasible to market 

 this product in a sound condition without then- use. No legit- 

 imate excuse, therefore, for the addition of any substance which 

 retards or inhibits bacterial development. Although the exig- 

 encies of certain branches of trade in milk products have, in 

 some cases, led to the adoption of regulations which permit 

 the addition of certain specified preservatives in quantities 

 not exceeding a specified limit, this practice should not be 

 encouraged, for, until it can be proved beyond reasonable 

 doubt that such preservatives are non-toxic, the public should 

 be safeguarded against these substances: public health should 

 be paramount to commercial interests and not sacrificed to 

 them. Unfortunately many statutes regarding the sophis- 

 tication of foodstuffs are even yet so framed as to place the onus 

 of proof as to damage to health upon the prosecutor and so give 

 the defendant the benefit of all doubts that may exist, but it is 

 pleasing to note that these are decreasing and that the present 



