L. MECHANICS AND ENGINEERING. 459 



amounts to 2520 atmospheres, being about 200 atmosplieres, 

 or 3000 pounds to the square inch, greater than the pressure 

 developed by the Prussian prismatic powder. Mittheilungen 

 Oesterr. Hydrogr. Bureau^ II., 13. 



RESEARCHES ON EXPLOSIVES. 



MM. Roux and Sarrau lately presented an interesting 

 memoir to the French Academy, on certain phenomena pre- 

 sented by explosives. They find that two kinds of explosions 

 can be manifested by the majority of explosive substances, 

 according as they are made to deflagrate (explosion of the 

 second order), or toi detonate, as by the percussion of ful- 

 minating powder (explosion of the first order). They find, 

 furthermore, that the energy of the explosion produced by the 

 same quantity of the explosive is very difierent in the two 

 cases, being invariably more powerful where detonation was 

 employed as the inciting cause, as will be seen from an in- 

 spection of the following table, in which the explosive energy 

 of gunpowder exploded in the ordinary manner is taken as 

 unity : 



Explosive Force. 

 - 



Name of Explosive. Second Order. First Order. 



Mercury fulminate 0.28 



Gunpowder 1 .00 4.34 



Nitro-glycerine 4.80 10.13 



Gun-cotton 3.00 6.46 



Picric acid 2.04 5.50 



Potassium picrate 1.82 5.31 



Barium " 1.71 5.50 



Strontium " 1.35 4.51 



Lead " 1.55 5.94 



Of these results, the most interesting and valuable is the 

 fact that the detonative explosion of gunpowder, induced by 

 the detonation of nitro-glycerine (which last is in turn deto- 

 nated by fulminate), produces an explosive energy more than 

 fourfold greater than that obtained by igniting powder in 

 the usual manner. 



STEAM FOG-TVniSTLES. 



It has been found by General Duane, of the United States 

 Engineers, in his experiments made to determine the best 

 form of boilers for steam fog signals, that as the steam used 



