DENSITY. 275 



The density is also sometimes determined by a hydrometer. 

 If this instrument be used, it should be tested in fats of known 

 density, and its indications thus controlled. A. Meyer states 

 that the height of the meniscus depends somewhat on the baro- 

 metric pressure, but the error due to this cause is not likely to 

 exceed the experimental error of reading. Should the tempera- 

 ture not* be exactly 37-8 0., a correction of 0-0007 for each 

 degree may be added for temperatures above and subtracted for 

 temperatures below, 37-8 C. 



100 



If it be desired to take apparent densities at ,-^0 "* glass, 



lo*o 



the instrument should be standardised at 15*5, and the density 

 determined as above. 



The author has used a bulb of specific gravity 0-865 at 15*5 

 for the purpose of determining rapidly an approximate density, 

 test A-tube is filled with the fat, the bulb dropped in, and the 

 tube placed in boiling water. If the bulb floats at the top, the 

 density is above 0-865 ; and if it sinks, it is below. This has 

 proved a fairly good rough test. 



The limits observed for pure butter are : 



Maximum. Minimum, Mean. 



At o4-S ' 9140 0-9094 0-9118 



O / "O 



100 

 At ^-^ (in glass) 0-8685 0-8650 0-8667 



The fats usually employed as adulterants have a density at 



37-8 100 



3^-go of 0-901 to 0-905, mean 0-903 ; and at j^~ (in glass) of 



0-860 to 0-863, mean 0-861. 



100 

 Certain oils have, however, a higher density ; thus, at =-= 5 



(in glass) 15 ' 5 



Palm-nut oil has a density ot . 



Coconut oil, 



Cotton-seed oil, 



Arachis oil, . 



Sesame oil, .... 



0-873 



0-874 



0-8725 



0-863 



0-8675 



Of these oils, palm-nut and coconut oils can be detected 

 readily (see Fat), while the other oils cannot be used alone, 

 but must be mixed with fats of less density to obtain the neces- 

 sary consistency. With the reservation that the oils mentioned 

 above would cause somewhat abnormal results, the determination 

 of the density of butter is a very useful test, and, though not 

 reliable as a single test, is of great use for corroborative purposes. 



