Flames of Carbonic Oxide and Hydrogen. 493 



The rate of propagation of the ignition in pure hydrogen mix- 

 ture is therefore 34 metres in the second*. 



It is to be supposed that the true rate found by the experiment is 

 somewhat too high, owing to the cooling which the stream of gas 

 is subjected to at the mouth of the exit-opening, and which makes 

 the desired value too small. 



Since the distance between the path of the spark and the sides 

 of the glass vessel (constructed of the dimensions given above) is 

 only 8*5 millims, we may conclude 



That the time which the whole of the gas takes to burn com- 

 pletely, and therefore also to reach the maximum temperature, 

 is not more than ^-qqq part of a second. 



The light of the spark was examined by means of a disk whose 

 rate of rotation is known, and provided with radiating segments. 

 Looking through this at a white surface illuminated by the light 

 from the exploding gases, the duration of the illumination is 

 found to be jfc of a second. 



Hence, whilst the maximum temperature is reached at the very 

 most in 40*00 °^ a sec 0110 '? the temperature during J3- of a 

 second appears to fall so little that the flame still produces a 

 dazzling light. 



It is therefore clear that, in the case of pure detonating gas, a 

 constant error in measuring the pressure is not to be feared. 

 These relations are less favourable in the case of the detonating 

 mixture with carbonic oxide, which possesses the very low rate 

 of not quite 1 metre in the second, but, on the other hand, seems 

 to cool very slowly indeed. Notwithstanding this, satisfactory 

 results can be obtained by measurements of pressure of this gas, 

 since we can scarcely doubt that the agreement between results 

 with this gas and those with hydrogen does not depend simply on 

 chance. The measurements of pressure were made in the fol- 

 lowing way : — The mixture of gases to be exploded is collected 

 over mercury in the exploding-vessel, fig. ], and filled up to a 

 definite point denoted by a file-mark ; the level of mercury in 

 the vessel is then made equal to that in the trough, and the 

 vessel is closed with the covering-plate, fig. 2. This consists of 

 a thick disk of mirror-glass with polished surface. To this a 

 second, iron plate is cemented, from which an iron pin passes for 

 the reception of the spark through a hole in the glass plate. 



* From these numbers we see that the velocities which are observed on 

 the sun's surface in the case of certain progressive luminous effects occur- 

 ring in given times, are altogether of a higher order than the velocities 

 with which chemical combinations occur in gaseous mixtures. The hypo- 

 theses according to which these solar phenomena are explained by chemical 

 processes must therefore undergo considerable limitation. 



