62 MARKET DAIRYING 
weeks. The tablets color the milk so that there can be 
no mistake about its unfitness for consumption. 
When .colorless preservatives are used, like ordinary 
formalin and corrosive sublimate, a little analine dye 
should be added to prevent mistaking the identity of 
milk treated with these preservatives. 
During’ the warm summer time the bichromate of 
potash is not as satisfactory as either of the other two 
preservatives mentioned, because of its comparative weak- 
ness and liability to interfere with the test when too much 
of it is used. When the bichromate is used in the ordi- 
nary solid form not more than a piece the size of a pea 
should be used, otherwise a good, clear test is not possible. 
For spring, fall, and winter use, however, bichromate of 
potash is excelled by no other preservative, either in 
cheapness, or safety and convenience in handling. 
Care of Composite Samples. It is a duty which the 
milk buyer owes his patrons to keep the sample jars 
carefully locked up in the refrigerator when not in use 
so as to prevent the possibility of anyone’s tampering with 
them. This will serve the additional purpose of excluding 
the light and heat from the samples, for they will keep 
but a short time when exposed to light and heat. 
When the sample jars are permitted to stand a few days 
without shaking, the cream which rises will dry and 
harden, especially that in contact with the sides of the 
jar, so that it becomes difficult to secure a fair sample 
on testing day without special treatment of the sample. 
This is prevented by giving the jar a rotary motion every 
time a sample of milk is added. 
It is important, too, that the covers of the jars fit tight, 
otherwise evaporation takes place, resulting in an in- 
creased test. In several instances the author has ob- 
