DETECTION OF ADULTERATION 55 



boric acid per looo c.c. Formaldehyde is an 

 efficient antiseptic. In the proportion of 0.125 

 gram to 1000 c.c, it will keep milk sweet for a 

 week. Hydrogen peroxid, ozone and dichro- 

 mates have been used. The almost universal 

 decree of sanitary authorities is that milk 

 must be free from any added material, but 

 owing to its comparatively high cost, liability 

 to decomposition and the marked characters 

 of even incipient decomposition, great tempta- 

 tion to use preservatives exists and any anti- 

 septic, not actively poisonous, may be used. It 

 has been found that milk drawn and marketed 

 under strict sanitary precautions wiU keep for 

 a considerable time, even at moderate tempera- 

 tures. The only permissible method of pre- 

 serving milk is by refrigeration. 



In addition to the descriptions of the detec- 

 tion and estimation of preservatives given below, 

 see also under "Cream." 



Formaldehyde. Hehner's Test. — Hehner found 

 that when milk containing formaldehyde is 

 mixed with sulfuric acid containing a trace 

 of a ferric compound, a distinct blue appears. 

 Richmond and Boseley showed that the delicacy 

 of the test is much increased if the milk is 

 diluted with an equal volume of water and 

 sulfuric acid of 90 to 94%, added so that it 

 forms a layer underneath the milk. Under 

 5 



