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Experiments on the explosive force of Oxygen and Hydrogen 

 Gases. By James Johnston, Esq. Communicated by the 

 Author. 



To the Editor of the Edinhtirgh Philosophical Journal, 



Sir, — In 1841 I took out a patent for obtaining motive power from 

 the explosive and condensing properties of oxygen and hydrogen gases. 

 In order to ascertain the power and length of stroke which those gases 

 would give when exploded in a cylinder, I commenced, on the 24:th April 

 1841, a set of experiments, of which I now give the results. 



The apparatus with which I made the experiments consisted of a strong 

 east-iron cylinder accurately bored, so that its diameter was exactly two 

 inches and thirteen-sixteenths of an inch. This diameter gives a surface 

 on the piston of six square inches. 



The piston was fitted very accurately into the cylinder. I have ascer- 

 tained it to work perfectly air-tight. On the top of the piston there is 

 a cross-head and spindle for placing weights upon. The ends of the 

 cross-head work in cast-iron guides. 



The gases are admitted to the cylinder by stop-cocks, and are ex- 

 ploded by an electric spark. 



I shall now describe the preliminary arrangements made before making 

 each experiment. 



I ascertained the weight of the piston, piston-rod, and other appen- 

 dages, which the gases must move when the piston is put in motion, to 

 be 9 lbs. 5 oz. 



I then ascertained, that, to overcome the friction of the piston, it re- 

 quired 5 lbs. 1 oz., together with its own weight ; therefore add 5 lbs, 

 1 oz. to 9 lb. 5 oz., and we have 14 lbs. 6 oz , the weight or force required 

 to overcome the friction of the piston. 



I now proceeded to load as follows the piston, so that I would give 

 the gases 5 lbs. per square inch of weight to lift. 



Weight of piston, ..... 9 lbs. 5 oz. 



Amount of friction of piston, . . . . 14 ... 6 ... 



Amount of weight required to make up the 5 lbs. per square inch, 6 ... 5 . , , 



Total weight, 30 lbs. oz. 



This gives 5 lbs. per square inch of weight, as there are six square 

 inches of surface on the piston. 



I measured the gases in the cylinder by the height to which I raised 

 the piston. Every inch of distance between the bottom of the cylinder 

 and the bottom of the piston holds six cubic inches. AVhen making the 

 experiments I always raised the piston to the height which I wished it 

 to be at, by placing under the ends of the arms of the cross-head pieces 

 of wood made for the purpose. After the piston was thus raised to its 

 required height, the apparatus was ready for the explosion, as the gases 

 were admitted at the pressure of the atmosphere at the time the piston 

 was raised. 



