172 MILK 



accomplished only after the cream has been heated to about 40 C. 

 The results will necessarily be too high, since water is lost through 

 evaporation. 



In order to avoid waste of cream small samples should be taken. 

 Enough cream for a duplicate test is sufficient; if excessive quanti- 

 ties are taken for testing, there is a material loss. Cream samples 

 should never be shaken, but mixed by a rotary motion. 



The Amount of Add Required for Cream Testing. When 18 

 grams of cream are used for a test an equal amount of acid is 

 added. When 9-gram charges are used the cream should be diluted 

 with an equal amount of water and then the usual amount of acid 

 added. Hunziker and Mills recommend the addition of enough 

 acid to the cream to produce a color in the mixture similar to that 

 of coffee to which cream has been added. The quantity of acid 

 need -not be measured, as the required amount varies with cream of 

 different richness. For a 9-gram charge 4 to 8 c:c. of acid will be 

 required, according to the per cent, of fat. A smaller amount of 

 acid will answer for cream testing than for milk testing, because 

 the acid reacts with the plasma solids, not with the fat, and con- 

 sequently the larger the amount of fat, the less the quantity of 

 acid necessary. 



Reading the Results. The reading should be taken at a temper- 

 ature of about 49 C. (120 F.). * If necessary the bottles must be 

 warmed in a water-bath. The temperature in testers run by steam 

 is liable to be too high and should be controlled so as to keep it 

 evenly at 50 to 55 C. A thermometer inserted through a hole 

 in the cover of the centrifuge will aid in regulating the tempera- 

 ture. 



According to Webster, the readings should be taken in this 

 manner: "Read from the bottom to the extreme top of the fat 

 column. Read the depth of the meniscus and deduct four-fifths 

 of it from the previous reading. When 9-gram bottles are used 

 0.2 per cent, should be added after the reading has been 

 doubled." 



Farrington and Woll state that the reading should extend 

 from the bottom of the lower meniscus to the top of the upper 

 meniscus. 



Shaw says, "the important difference between reading the 

 cream test and the rnilk test is that in the cream test the fat column 

 included is from the bottom of the lower meniscus to the bottom, 

 not the top, of the upper meniscus." 



These differences of opinion have arisen since it has been found 

 that all the fat is not brought within the graduated portion of the 

 neck. A small amount adheres to the inside of the bulb of the 

 bottle and small fat globules remain suspended in the acid milk mix- 



