i:\ri.osioNs OF COAI.-UAS AM> AII;. 



391 



fig. 12). Water 1 cm. thick entirely cuts off all radiation of wave-length greater 

 than 1'2/x or 1'3/u, and is most transparent in the visible part of the spectrum (0'4/u 

 to 07^).* The water-cell therefore cuts off all the radiation peculiar to heated CO 2 

 itinl water vapour (which is of wave-length between 2/ and 5ft) and transmits 

 practically only the luminous radiation. The water-cell continues to transmit 

 radiation for about one-tenth of a second after the attainment of maximum pressure, 

 and it seems probable that the mixture is luminous during this period.! The total 

 loss of heat in tin- explosion of this mixture due to the emission of luminous radiation 

 is ;il>out 0'25 per cent, of its heat of combustion. 



Table VIII. has been prepared from tin- Curves H in fig. 8. These curves refer to 

 experiments made with a 25'4-per-cent. mixture of hydrogen and air. The radiation 

 curve is the mean of those taken with the bolometer in positions A, B, and C on the 

 end cover. The hydrogen used in these experiments was supplied by the British 

 Oxygen Company, guaranteed 98 per cent. pure. 



TABLE VIII. 25'4-per-cent. Mixture of Hydrogen and Air. Initial Pressure, 



Atmospheric. 



Heat of Combustion of Hydrogen in Vessel = 1C, 320 Calories. 



The total amount of radiation emitted up to the moment of maximum pressure 

 amounts to 0'5 per cent, of its heat of combustion, the maximum temperature l)eing 

 2400 C. (abs.) and the time of explosion 0'017 second. A 1 5-per-cent. mixture of 

 coal-gas and air whose maximum temperature also reached 2400 C. (aim.) emitted 

 up to the moment of maximum pressure rather more than 3 per cent, of its heat of 

 combustion, the time of explosion in this case being 0'05 second. 



* For the transmission spectrum of water, see E. F. NICHOL'S paper, ' Phys. Rev.,' I., p. 1, 1896. 



t On looking at the explosion of a 15-per-cent. mixture in the same vessel through the window, the 

 bright flash appeared to the eye to last for about \ second (the " time of explosion " of the mixture in the 

 vessel being only J s second). Of course if water transmits even a small projx>rtion of radiation of longer 

 wave-length the above statement is not justifiable. 



