406 Bulletin 92 



The gravity of oils is measured commonly on the Baume scale. 



The formula for conversion is as follows: 



140 



Specific gravity ( decimal )= 



ISO-j-Baume value 



Specific gravity is obtained readily by means of a hydrometer, a 

 small instrument costing one or two dollars. Each farmer or com- 

 munity of farmers should own one. A hydrometer with range from 

 35° B. to 70° B. is recommended, since this range includes gas oils, 

 kerosene, and gasoline, and is found on one of the standard commer- 

 cial hydrometers. 



While taking the specific gravity, the temperature of the oil 

 should be obtained also. A correction can be applied to reduce the 

 specific gravity to what it would be at 60° F., the standard tempera- 

 ture. Approximate rules for this correction are as follows : 



For gasoline, allow 1° Baume for each 10° F. 



For tops and similar oils of about 40° B., allow 1° Baume for 

 each 12° F. 



For Calol diesel fuel oil and similar oils of about 25° B., allow 

 1° Baume for each 15° F, 



The correction is to be added to the reading of the hydrometer if 

 the temperature of the oil is below 60° F. when tested, and subtracted 

 if the temperature is above 60° F. 



There has been considerable condemnation of the specific gravity 

 test by some oil companies, on the ground that it does not show the 

 fitness of an oil for engine service. The test is of great value, how- 

 ever, and it is the easiest test to make, and should be used generally. 

 The ultimate and best test is the experience with an oil in actual 

 service. So long as oils come from the same field, as, for example, 

 the southern California field, then the average volatility, and the fitness 

 of a shipment are indicated usually by the specific gravity. That is, hav- 

 ing had experience with gas oils of various densities, a purchaser can 

 take the specific gravity (and perhaps the flash i:)oint) and then know 

 whether or not the oil is satisfactory. When oils come from an untried 

 field, then further tests are necessary, either the distillation test or the 

 test of actual service. 



FLASH POINT 



The flash point is the temperature at which vapor is given off in 

 such quantity that it flashes when exposed to an open flame. The 



