494 Prof. K. Bunsen on the Temperature of the 



The glass plate is covered with a little olive-oil and then brought 

 under the exploding-vessel, to the polished mouth of which it is 

 made to adhere by gentle rubbing. The vessel thus closed air- 

 tight is brought out of the trough, provided with the little glass 

 ring, fig. 3, and arranged as seen in fig. 4. This glass ring, 

 which is filled with water, is placed water-tight on the caoutchouc 

 washer attached to the exploding-vessel. For the measurement 

 of the pressure itself, the lever arrangement represented in fig. 4 

 is used. The fixed weight (a) serves to balance the longer arm 

 of the lever, along whose divisions the weight (b) can be moved 

 so as to be able to vary at pleasure the pressure with which the 

 vessel is closed. The iron plate of the exploding-vessel, on which 

 the rod (d) from the lever presses, is provided with a slight hol- 

 low at the centre, into which the conical point of d can be placed 

 at all times in the same position, c is a strip of tinfoil which is 

 in contact with a platinum wire sealed air-tight through the 

 bottom of the exploding-vessel ; and this wire is in contact with 

 the mercury contained in the vessel. In order, then, to pass a 

 spark through the whole column of gas, it is only necessary to 

 connect one wire from the coil with the metal lever, the other 

 with the tinfoil. When the pressure caused by the burning of 

 the gas is less than that exerted by the lever-arm on the glass 

 plate, the gas burns without any distinctly audible noise, and 

 without setting the water in the glass funnel in motion ; if the 

 contrary is the case, the water is forcibly thrown out and a loud 

 explosion occurs. The degrees of pressure by which, on the one 

 hand, quiet burning, and, on the other, burning with explosion, 

 occurs, are so distinctly marked, that the mean of a few experi- 

 ments in which both points are noted may be considered to be the 

 pressure sought. This is shown in the following experiments : — 



Cyanogen with air : pressure, in J" 11*01 quiet burning, 



atmospheres . . . . . \_10*90 loud explosion. 

 Carbonic oxide with air : pressure, f 7*34 quiet burning, 



in atmospheres .... (_ 7*22 loud explosion. 

 Carbonic oxide with oxygen: J" 10*20 quiet burning, 



pressure, in atmospheres . \ 10*04 loud explosion. 

 Hydrogen with oxygen: pres- j 9*56 quiet burning, 



sure, in atmospheres . . \_ 9*46 loud explosion. 



It is scarcely necessary to say that the pressure to which the 

 gases were subjected when the exploding-vessel was closed must 

 be added to that exerted on the lever-arm. There is, besides, 

 another correction to be made for the adhesion of the glass plate 

 to the vessel. The pressure which this exerts must be overcome 

 by the explosion, and it must therefore be added to that measured 

 on the lever. The force of the adhesion, as is well known, is to 



