76 MODERN METHODS OF TESTING MILK 



bottles are added. It is more convenient after a little 

 practice to weigh exactly 9 or i8 grams than to run 

 in an approximate amount of cream and weigh that 

 accurately. 



In case one uses any amount less than 18 grams for 

 a sample, it is necessary to correct as follow^s the per 

 cent, of fat read : Divide 18 by the number of grams 

 of cream used and multiply the result by the per cent, 

 of fat read in the test. For example, one uses 13.5 

 grams of cream and the result reads 15.6 per cent, of 

 fat. Divide 18 by 13.5, which gives 1.33, and multiply 

 this by 15.6, which equals 20.8 per cent., the true per- 

 centage of fat in the sample. 



SPECIAL POINTS ABOUT TESTING CREAM 



When one uses 18 grams of cream in one test-bot- 

 tle, the operation is completed as in testing milk. 

 When one uses less than 18 grams in one test-bottle, 

 enough water is added to make the volume about 18 

 cc. Thus, when an 18-gram sample is divided be- 

 tween two bottles, or a 9-gram sample in one bottle 

 is used, we add 9 cc. of water to the cream, mix them 

 thoroughly and then proceed as usual. The water and 

 cream should always be well mixed before adding 

 acid. 



When it is difficult to get a clear column of fat, it 

 may be remedied by the use of a little less acid, the 

 exact amount to be found by trial. In general, the 

 richer the cream, the less acid is required, 15 cc. often 

 being enough. The full amount of acid is used when- 

 ever the cream is diluted w^ith water before adding 

 acid, as in the case of taking a 9-gram sample, or di- 

 viding an 18-gram sample between two cream-bottles. 



