8 A DAIRY LABORATORY GUIDE 



also coming into common use. These bottles give 

 the reading direct without any computation. In 

 testing 9 grams one would naturally use one-half 

 "the usual amount of sulphuric acid. On account, 

 however, of the large proportion of fat present, the 

 acid is liable to char the fat ; and for this reason it 

 is better to add approximately 9 grams of water 

 and then add a little less than the usual amount of 

 acid. 



Butter is tested in the cream bottles, from 3 to 4 

 grams being used for the test. Enough warm 

 water is added to bring the sample up to approx- 

 imately 18 grams, and from 10 to 12 cc. of the sul- 

 phuric acid are used. 



Cheese is also tested in the cream bottle, 4 to 5 

 grams being used. The cheese must first be minced 

 with a knife as fine as possible in order to make it 

 possible for the acid to dissolve all of the casein. 

 After the cheese is weighed into the bottle, about 

 5 cc. of hot water are added and the mixture shaken 

 vigorously for two or three minutes. This softens 

 the casein. Enough hot water is then added to 

 bring the sample to approximately 18 grams. The 

 sample is again shaken for two or three minutes, 

 and the ordinary amount of H 2 SO4 is then added. 

 If the cheese is old and dry, 2 or 3 cc. of H 2 SO4 in 

 excess of the usual amount are sometimes necessary 

 to dissolve the casein. In mincing the cheese the 

 sample should not be allowed to dry out any more 

 than is absolutely necessary. 



In the cases of both the butter and the cheese, 

 the results obtained must be reduced to an 1 8-gram 

 basis, because the bottles are graduated for that 

 amount. This can be done by dividing the per cent 

 obtained by the number of grams used and multiply 

 the quotient by 18. 



