66 MILK HYGIENE 



If potassium bichromate be present, the mixture has a 

 yellow or reddish-yellow color. 



e. Formalin or formol is a 40 per cent, solution in 

 water of formaldehyde. It is a superior disinfectant 

 and is being employed more and more. The presence of 

 0.008 per cent, formaldehyde (^=0.02 per cent, formalin) 

 is able to check coagulation of milk for 100 hours. The 

 addition of formalin causes no change in the fats, there- 

 fore it may be used to advantage in samples taken for 

 fat determinations. Formaldehyde has, however, a very 

 decided effect on albumin and as it has a deadly effect on 

 the protoplasma of bacteria, so it is also a powerful poi- 

 son for the animal cells and tissues. Investigations by 

 Annett have proven that the addition of formalin to 

 milk, even in the proportion of 1 to 50,000 may be injur- 

 ious, especially for young animals, and even to the point 

 of causing death. The addition of formalin to milk 

 should therefore be rigorously prohibited. 



There are many ways of detecting f ormalia in milk : 



1. 100 c.c. of milk are distilled; when about 20 c.e. 

 are evaporated, the distillate is tested by the addition 

 of 5 drops of ammoniacal solution of silver nitrate (1 gr. 

 silver nitrate is dissolved in 30 parts of water and 

 enough diluted ammonia water is added so that the sedi- 

 ment which appears is again dissolved ; then it is diluted 

 to 50 c.c). After the tube has been shaken, it is left 

 standing in the dark for some hours. The presence of 

 formalin is shown by a black sediment or by a black color 

 of the liquid (Thompson). 



2. In many cases it is sufficient to add the silver solu- 

 tion directly to the milk, since this either colors it black 

 at once or gives it a brownish color if left standing in 

 the dark. 



3. According to Lebbins, a test may be made by the 

 addition of a little resorcin and 50 per cent, solution of 



