165 



were invariably collected as naphtha until it reached a tem- 

 perature of 120°, then it is plain that all collected from the 

 distillation at a higher point than this, will be secure against 

 all explosions when not exposed to as high a heat as 120°. 

 And since, even in a burning lamp the oil never reaches so 

 high a point, it may be termed absolutely safe. Not so, 

 however, if the oil is not thus honestly separated. Since 

 naphtha is commercially a much less valuable product than 

 burning oil, there is the greatest temptation for manufac- 

 turers to increase the quantity of their oil by collecting 

 as oil what ought rather to be classed as naphtha. And the 

 temptation to this dangerous expedient is greater, inasmuch 

 as the oil when mingled with a certain proportion of 

 naphtha actually burns with a brighter flame than without 

 it. 



It may be observed in this connection that specific gravi- 

 ty is not a sufficient test of the quality of rock oils. The 

 refined oil from different wells differs somewhat in this re- 

 spect, without differing in regard to the point at which they 

 may be inflamed. Besides, if specific gravity were the 

 only test, the dishonesty of mixing naphtha with the burn- 

 ing oil, could easily be concealed by adding a sufficient 

 quantity of the heavier lubricating oil to restore the dimin- 

 ished density. 



The oil of different refineries varies very much in respect 

 to the point at which it may be inflamed from a lighted 

 match. Experiments upon this point have shown that the 

 products of some extensive establishments will kindle at a 

 temperature as low as 85°. It may be readily seen that such 

 oil exposed to the temperature of a warm room, or even 

 exposed to the heat of the summer sun, is liable to the dan- 

 ger of explosion. And yet such oil in all external aspects, 

 and even in specific gravity may be undistinguishable from 

 the best and safest oil. It may in general be said that the 

 safest oil is that which has the least odor, because the odor 

 seems mostly connected with the naphtha, and the presence 



\Trans. iv.] 23 



