504 WRITINGS OF JOSEPH HENRY. [1875 



formerly adopted in England for specific gravity is 62° F, ; 

 but in the case of petroleum the temperature of 60° has been 

 adopted in this country and England. In the first series of 

 experiments made with the oils in question, the weighing 

 was conducted at a temperature of 74°, as we have said, 

 namely that of the atmosphere at the time. A series of 

 experiments at a lower temperature was afterward made, in 

 order to obtain a correction by which to reduce the specific 

 gravity first obtained, to that of a temperature of 60° ; but as 

 each oil exhibits a different rate of expansion by heat, the 

 process became very laborious. Experiments were therefore 

 made to determine the correctness of indication of the specific 

 gravity of the oils by means of a hydrometer. This was found 

 to diff'er from that obtained by weighing within one per cent., 

 and was therefore concluded to be sufficiently accurate for 

 practical purposes. 



To obtain the specific gravity of the oils by means of a 

 hydrometer, a vessel of a depth of about 14 inches (contain- 

 ing say 10 gallons of water,) is provided; into this are intro- 

 duced several glass cylinders containing the oil, and into these 

 cylinders the hydrometers are plunged, the level of the oil 

 being so far above the water that the under contact of the 

 surface of the liquid with the scale may be observed. Before 

 inserting the glass cylinders containing the oils into this 

 water-bath, the liquid is brought to the temperature of 60° 

 by mixing ice-water with it, at which temperature it may be 

 kept for a long time, on account of the large quantity of the 

 liquid and the great specific heat of the water. A change of 

 temperature may be prevented by occasionally adding a 

 small quantity of ice-cold water, care being taken to mingle 

 the mixture by stirring. By this process the specific gravity 

 at 60° of a large number of samples may be obtained in a 

 comparatively short time. In this country and England 

 the density or relative weight of petroleum oils is generally 

 expressed in terms of the arbitrary scale of Beaume, instead 

 of that of the specific gravity. The following table gives the 

 equivalent of the Beaum6 scale in terms of specific gravity: 



