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 formalin in milk : 



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

 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 



