DETECTION OF ADULTERATION 55 
boric acid per 1000 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 will 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 
