1275] WRITINGS OF JOSEPH HENRY. 



Beaume's hydrometer for liquids lighter than water. 



505 



Another test to which the mineral oil was subjected was 

 that of a reduction of temperature. For this purpose the 

 samples were placed in an air-bath reduced to the tempera- 

 ture of 25° F. At this temperature several of the oils exhib- 

 ited a thickened condition, especially those of the higher fire- 

 test. The apparatus used for this purpose was the same as 

 that previously described as employed in the case of lard oil. 



The next test to which the oil was subjected was that of 

 its liquidity. This test is of some importance in regard to 

 lamps in which the oil is pumped up by machinery, and 

 also as to the solid matter in the oil. It therefore gives a 

 characteristic of the oil which with others serves to deter- 

 mine its degree of impurity. For this purpose the same 

 method was employed as that described for determining the 

 liquidity of lard oil. The liquidity exhibited by this pro- 

 cess varied greatly in different oils. 



All the experiments on the flowing of the oils were made at 

 the temperature of the air, which was from 72° to 74°. In 

 this case, as with lard oil, a marked difference was found in 

 the time of flowing at different temperatures, and hence for 

 comparison the experiments should be made at a standard 

 temperature. 



Another experiment was made to ascertain whether oils of 



