MECHANICS AND USEFUL ARTS. 121 



Wood charcoal may be used instead of mineral coal, but it is not 

 go good. Nitrate of soda may also be used in place of tlie nitrate 

 of potash." 



Picric Acid. — In a lecture delivered before the Society for the 

 Encouragement of National Industry in France, Dr. Calvert spoke 

 of a curious application which has been made of the explosive 

 property of the salts of this acid. During the last few years, the 

 Ijicrate of potassium has been employed in great quantities by 

 Mr. J. Whitworth, for charging the bombs for destroying the iron 

 plating of ships. When the projectiles thus prepared strike the 

 iron masses, the enormous force with which they are expelled 

 from the gun is instantaneously converted into heat, and to such 

 an extent that the ball becomes red-hot, the heat decomposes the 

 picrate of potash, and a violent explosion ensues, owing to the 

 enormous quantities of vapors and gases which are thus produced 

 in an instant of time. 



Nitro-glycerine. — The London "Chemical News'' says that 

 when nitro-glycerine is dissolved in 2 or 3 times its bulk of 

 methylated spirit it is quite inexplosive, and when required for 

 use, the addition of water will precipitate the oil, the layer of wa- 

 ter and spirit merely requiring decanting off. The nitro-glycerine, 

 separated in this way, possesses explosive properties quite as ac- 

 tive as the original oil, which, indeed, is frequently rather improved 

 than otherwise by the ti'eatment. 



Penetration of Cannon Balls. — The fact has been satisfactorily 

 demonstrated at the Shoeburyness trials, that a cannon-ball will 

 penetrate a target with much greater ease with a range of 200 

 yards than with a range of 70 yards. The supposed explanation 

 for this fact is that the shot "wobbles" a little on leaving the 

 gun, and requires time, and consequently space, to settle down 

 to a steady whirl. The fact that the holes made at 70 yards are 

 larger than those made at 200 yards, supports this hypothesis. 



Gatling Gun. — It appears that the Gatling revolving gun, de- ' 

 cribed in "Annual of Scientific Discovery " for 1868, pp. 115, 116, 

 is to be very generally introduced into European armies. Accord- 

 ing to the Augsburg "Gazette," the agents in Carlsruhe have 

 received orders for 1,000 of these guns. Of this number, 400 are 

 designed for France, and 200 for Russia, the remainder being 

 equally distributed between Austria, Italy, Belgium, and Hol- 

 land. , 



SUBMARINE DRILL. 



The improved submarine drill, recently perfected in New York, 

 for use in removing obstructions at Hell Gate, is acknowledged by 

 experts to be the best ever invented. The machine is in the shape 

 of a " mushroom anchor," or half of a sphere. It is about 7 feet 

 in diameter at the bottom, and weighs 5 tons. Inside of the iron 

 frame, which is water-tight, are placed 2 engines of about 5 horse- 

 power. They are supplied with steam by means of a flexible 

 tube, vvhich is attached to a boiler on board a tug. The "an- 

 il 



