338 EXPERIMENTS ON THE RELATION 



acid, while the latter contains both. This supposition, which 

 the chloridic theory compels us to make, must surely be rec- 

 koned somewhat violent. 



Description of an Apparatus for the Analysis of Gaseous Matter 



by Explosion. 



The analysis of combustible gases, and supporters of com- 

 bustion, reciprocally, by explosion, with the electric spark, 

 furnishes, when it can be applied, one of the speediest and 

 most elegant methods of chemical research. The risk of fai- 

 lure to which the chemist is exposed, in operating with the 

 simple tube, from the ejection of the mercury, and escape or 

 introduction of air; or of injury from the bursting of the glass, 

 by the forcible expansion of some gaseous mixtures, has given 

 rise to several modifications of apparatus. 



Volta's mechanism, which is employed very much at Paris, 

 is complex and expensive*, while it is hardly applicable to ex- 

 periments over mercury. Mr Pepys's ingenious contrivance, 

 in which the glass-tube is connected with a metallic spring, to 

 diminish the shock of explosion, is liable also to some of the 

 above objections. 



A very simple form of instrument occurred to me about two 

 years ago, in which the atmospheric air, the most elastic and 

 economical of all springs, is employed to receive and deaden 

 the recoil. Having frequently used it since that time, I can 



now 



* The price of the apparatus is about three guineas. 



