160 PROCEEDINGS OF SECTION B. 



22.— THE FREEZING POINT OF MILK : ITS USE IN THE 

 DETECTION OF ADDED \VATER. 



By J. BROWNLIE HENDERSON, F.I.C., Government Analyst, Brisbane. 



Since the beginning of food analysis there has been a very keen 

 search for a method of determining with certainty whether any sample 

 of milk has or has not been adulterated by the addition of water. 



Until recent years it was quite impossible in many cases to 

 certify to the addition of water, though the analyst was morally 

 cei-tain it had been added. The adoption of the 8'5 per cent, solids 

 not fat legal standard, instead of tending to keep the milk supply 

 pure, has largely resulted in the milk (which is as often over 9 per cent, 

 solids not fat as under 8"5 per cent.) being watered down to this low 

 standard. In fact, a defendant has in court in England stated that 

 he did not add more water than '' the G-overnment allowance." 



Many methods have been proposed for the determination of this 

 vexed question, but owing to the great variation in the quality of the 

 genuine milk from various cows little headway has been made until 

 recently. 



The well known fact that the composition of milk serum does 

 not vary much, and from the nature of its origin from the blood of 

 the cow cannot vary much, has opened up what seems to be a good 

 path leading to the solution of the problem. 



There are several methods of dealing with the question in this 

 direction, and these may be summarised as follows : — 



(a) Determination of the specific gravity of the milk serum; 



- (b) Determination of the electrical conductivity of the milk 

 serum ; 



(c) Determination of the refractive index with the Zeiss 



Immersion Refractometer ; 



(d) Determination of the freezing point of the miUc. 



Of these methods the first three require the preparation of the 

 milk serum, whereas the freezing point can be determined in the pre- 

 sence of the fat, which, not being in solution, does not affect the 

 freezing point. This gives the freezing point method a very great 

 advantage over the others in a working laboratory where many 

 samples have to be done in a day. 



So far as I can learn, sufficient work has not yet been done on 

 the specific gravity and the electrical conductivity of the milk serum 

 to make either of these methods useful in the ordinary working 

 laboratory. The refractive index of the milk serum, as determined 

 by the Zeiss Immersion Refractometer, has however given results 

 which promise fairly well. Unfortunately, the method is tedious, 

 owing to the trouble involved in preparing the serum, and to the great 

 difficulty, especially in warmer climates, in keeping the solutions 

 exactly at the stated temperature of 17"5° C. As even 0"2° C. 

 makes an appreciable difference in the readings, anyone who has 



