The Density at 140° F. of the Materials Expressed as Fat by Various Volumetric Tests of Cream

The density of the material comprising the fat columns in the various volumetric tests has received very little attention.This is undoubtedly due to the fact that the procedures of the tests have usually been adjusted so that the results will agree with the official method.There has been some investigation as to the absolute accuracy of some of the rapid methods of testing dairy products for fat.The Babcock test bottles are calibrated for fat of a definite density at a definite temperature.Several modifications of the Babcock procedure have been proposed.It seems obvious that a modification using alcohol would give a fat column of a density different from that of a test using acid.Babcock (1) in devising his test bottle assumed the specific gravity of the fat to be 0.9000 at 120 ° F.He did not believe that a variation in temperature of reading from 110 to 150 ° F. would materially affect the results for milk although he recommended using the higher temperature.The difference for the 40 degree range was given as being less than 0.1 per cent for a 5 per cent milk test.In 1891 Farrington (2) obtained the greatest accuracy compared to gravimetric methods if the fat column in the Babcock milk test was read at 140 ° F.The directions for testing cream were likewise lax in spite of the greater differences that were bound to occur.Webster (3) in 1904 reported the density of fat to be 0.9004 at 100 ° F., but by weighing a definite amount of fat into a test bottle he was able to account for all of it only by reading at 120 ° F. A little later Hunziker, Spitzer, Mills and Crane (4) insisted that the correct reading temperature was 135 ° F. for that was the temperature at which the fat had a specific gravity of 0.9000.Then Ross and McInerney (5) recommended a reading temperature between 140 ° and 150 ° F., obtaining better checks with ether extraction at 150 ° F., but for milk they reported that there was no difference by reading at either 100 ° or 146 ° F. Bailey ( 6) disagreed with all previous investigators when he reported that all density measurements at Iowa State College showed the density of butterfat to be about 0.8974 at 120 ° F.He states that the density varies by 0.00038 per degree F. This gives a density of 0.9000 at about 113 ° F. Hepburn (7) used a temperature of 125 to 130 ° F. for his modified Babcock test for butter.Dahlberg (8) found the specific gravity to be 0.8943 at 132 ° F., however he