656 



REPORT — 1900. 



All experiments recorded in the present communication refer to the 500 c.c. 

 spherical enclosure. 



The Pressure Gauges. — Two distinct gauges are used. The first measures the 

 maximum pressure attained and in principle is similar to Bunsen's original 

 apparatus. A piston lifts or does not lift according to -whether the explosive 

 pressure does or does not rise above the pressure corresponding to the weight with 

 which the piston is held down. In the present case, however, to diminish the 

 inertia of the system, the weights are replaced by a gaseous pressure acting on the 

 opposite end of the piston. The areas of the two piston heads being in the ratio of 

 50 to 1, an explosive pressure of 500 atmospheres is exactly balanced by a gaseous 

 pressure of 10 atmospheres acting on the other side of this equilibrium valve. To 

 render the action of the apparatus as rapid as possible, the travel of the piston is 

 limited by means of a micrometer screw to two or three thousandths of an inch. 

 The piston, on coming in contact with this micrometer screw, closes an electric 

 circuit communicating with an indicator. As an example of the method a series 

 of observations are given in the table. 



Table. 



The second measuring apparatus is in principle the same as the well-kno-wn 

 steam-engine indicator. The ordinary spring is, however, replaced by a brass 

 cylinder. The only motion which the piston can make is therefore that allowed by 

 the elastic compression of the metal. The time period of the system has not yet 

 been measured, but from the diagrams recorded, it is evidently below one five- 

 thousandth of a second. The maximum motion of the piston is less than one 

 thousandth of an inch. The motion of the piston, magnified to the desired extent 

 by a special device, is photographed on the cylinder of a I'apidly revolving 

 chronograph. 



The scale of time on the indicator card thus obtained can be varied from one 

 hundredth of a second per millimetre to one five-thousandth of a second per 

 millimetre. 



The Results obtained. — The records show a rapid initial rise of pressure, the 

 rate decreasing as the temperature of dissociation is approached. It is intended 

 to obtain a series of these indicator diagrams for initial pressures varying between 

 10 and 200 atmospheres. 



Many years ago Bunsen found that a mixture of oxygen and hydrogen fired at 

 atmospheric pressure gave an explosive pressure of 9-6 atmospheres. The present 

 experiments show that this ratio is still substantially correct up to initial pressures 

 of 42 atmospheres, the ratio actually given by Table I. being 1006. 



The ratio diminishes but slowly as the proportion of explosive gas to non- 

 explosive gas decreases. A mixture of H.^O and oxygen, containing but 49 per 

 cent, of explosive gas, still gives an explosive pressure of 319 atmospheres when 

 fired at an initial pressure of 42 atmospheres, the ratio being therefore 7-6. 



Under the same conditions a mixture containing 28-7 percent, of explosive gas 

 gives a ratio of 616. Finally, a mixture containing only 12 per cent, of H^O is 

 not explosive. 



As will be seen, even the few results that have as yet been obtained raise 

 many interesting questions, but with the limited data which as yet are available it 

 would be unwise to attempt any general discussion of the results. 



