328 MILK AND CREAM TESTING 



with the measure. When these have been run out in the usual 

 manner the quantity of acid used in the test showing up best, 

 will be nearly, if not quite, the quantity thereafter to be used 

 with that particular shipment of acid. 



Care of Acid. — Sulfuric acid has a very great affinity for 

 water. If the bottle is left uncorked, moisture will be taken in 

 from the air continually and far more rapidly than one would 

 suspect. Such diluted acid may even have lost its strength to such 

 an extent as to become useless in testing. A rubber plug should 

 be used in preference to one made of cork, though one made 

 of glass is best. If the ordinary cork is used for even a few 

 days, particles of charred substance will be found floating in the 

 acid and will introduce slight, annoying errors in the test made. 

 ^Neither light, nor heat, nor cold affects the acid, provided it is not 

 used when too hot nor too cold. 



Temperature to Use — Hot or warm acid is far more active 

 than the same when cool. Many samples of milk have been 

 charred from using acid which had stood around the dairy room 

 in summer and used without first being cooled. For best results 

 the milk and the acid should not have a temperature much below 

 55 nor above 65 degrees; F. It is often desirable, therefore, to 

 keep the acid in the basement ice chest, or to set into cold water 

 for a time before using. 



Water. — If hard water, that is water containing a consider- 

 able quantity of lime, is used there is great likelihood indeed, 

 that chemical reaction following will cause a moss-like mass to be 

 formed in the neck of the bottle through which fat will be dis- 

 tributed. It will be manifestly incorrect to include all of the 

 foreign substance as fat, yet to exclude all of it introduces a 

 yet greater error. 



Soft water, that is, rain water or snow water, or better yet, 

 condensed steam will be found most desirable. In case it is 

 impossible to obtain such soft water, ordinary hard water may be 

 treated in such a way as to purify it and yet not introduce an 

 error in the test. This is best done by adding a small quantity 

 of hydrochloric acid to the water. If no hydrochloric acid is 

 obtainable ordinary sulfuric or testing acid may be used 

 instead. One acid measure of acid mixed with half a pint of 



