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been entirely agreed in settling the modes of determining 

 the comparative safety or danger of different specimens. 



We know that the vapor arising from burning fluid when 

 mixed with a portion of air will explode with violence. 

 Common coal gas will do the same thing. And it has been 

 well ascertained that the unrefined rock oil, and even cer- 

 tain brands of refined will give off a vapor, which when 

 mingled with air will explode. It therefore becomes a most 

 important enquiry to determine the circumstances and pro- 

 perties which render explosions possible, and to find the 

 means of obviating them. 



When discussing the mode of refining the crude Petro- 

 leum, we pointed out that the first product that was expelled 

 by the second distillation, was a light, volatile, exceedingly 

 inflammable fluid termed naphtha. In the refineries of best 

 repute, all the oil expelled below 120° is collected as naph- 

 tha. If we examine this fluid we shall find that a lighted 

 match touched to it, will instantly ignite it at ordinary tem- 

 peratures, that if the vapor which arises from it be mixed 

 with air, it will explode like that of burning fluid. On the 

 contrary, if the same experiments be tried with good refined 

 Petroleum, no such results follow. A lighted match 

 plunged in it is instantly extinguished, as it would be in 

 sperm oil ; no vapor escapes that can be collected or ex- 

 ploded. The explosion is always consequent on the forma- 

 tion of vapor. Sperm oil does not explode, because no va- 

 por is given off. Good refined Petroleum does not explode, 

 because at the ordinary temperatures to which it is exposed, 

 no sensible vapor is given off. Naphtha does explode be- 

 cause at ordinary temperatures, and much more so when the 

 temperature is elevated, vapor is rapidly formed at its sur- 

 face. A fluid therefore, is only dangerous when exposed to 

 a temperature at which a vapor rises from its surface. 

 And this fact is ascertainable by determining the tempera- 

 ture at which it will take fire from a lighted match. 



If all the fluid obtained from distilling crude Petroleum, 



