MR. W. T. DAVID ON THK RADIATION IN 



An allowance of 5 per cent, has been made for the absorption of the fluorite, but 

 no allowance has been made for the absorption of the other diathermanous substances. 



The quartz plate transmits about 50 per cent, of the total radiation. The Bunsen 

 flame has two strong emission bands whose maxima are at 2'8/x and 4'4 / . The 4'4yu 

 band is due to CO 2 alone ; the 2'8/x band is due to water vapour and also to CO 2 . 

 The quartz plate (6 mm. thick) would transmit about 70 per cent, of the 2'8/x band 

 and would almost entirely cut oft* the 4'4/x band.* It is highly probable, however, 

 that with the high pressures in explosions the bands broaden out, for SCHAEFER has 

 shown that there is a widening of the absorption bands of CO 3 when the pressure is 

 increased. If the emission and absorption bands are similar the quartz will transmit 

 from 10 per cent, to 20 per cent, of the 4'4/u bands, t The 2'8yot band also broadens 

 out and the quartz transmits about 65 per cent, of it.J It is not difficult from these 

 observations to estimate roughly the proportion emitted by the water vapour and by 

 the CO* lloughly, one may take it, the hydrogen emits from 50 per cent, to 60 per 

 cent, of the total radiation, the remainder being, of course, emitted by CO 2 . There is 

 nearly two and a half times as much water vapour present in the mixture as there is 

 CO a , so that, speaking somewhat loosely, the CO 2 emits about twice as strongly as the 

 water vapour does volume for volume. 



Bolometric measurements with the window of quartz were also made in the 

 different positions A, B, and C, and also with different strengths of mixtures, and in 

 each case the radiation transmitted through the quartz was always the same 

 proportion of that measured with the fluorite window. 



The plate glass (|- in. thick) transmits about one-third of the total radiation 

 emitted by the gaseous mixture. The glass probably cuts oft' most of the radiation 

 emitted by CO 3 and transmits about 50 per cent, of that emitted by the water 

 vapour. 



The water-cell almost entirely cuts off all the radiation emitted by the gas (see 



* See ' Transmission Spectrum of Quartz, Coblentz, Infra-Red Spectra,' Part VI., p. 45. 



t See absorption spectrum curves of CO 2 in SCHAEFEK'S paper (' Ann. der Phys.,' 16, 1., p. 93), and also 

 the transmission spectrum of quartz. 



t This result was obtained from a comparison of the amounts of radiation from a hydrogen and air 

 mixture received by the bolometer when it was protected first by the plate of fluorite and then by the 

 plate of quartz. This gaseous mixture contained after explosion only steam and nitrogen, so that the 

 radiation emitted was almost entirely of wave-length in the neighbourhood of 2 -8/1. 



The radiation emitted by the gaseous mixture is almost entirely due to the H 2 O and CO* which it 

 contains. The mixture contains about 8 '5 per cent, of C0 2 and 20 per cent, of H 2 O, the remainder being 

 almost entirely N. 



It is interesting to compare this result with those of R. VON HKLMHOI/T/ on the radiation from 

 hydrogen, carbon monoxide, marsh gas, ethylene, and coal-gas flames. He found that the CO 2 produced 

 in the CO flame emitted about 2 "4 times as strongly as an equal volume of water vapour produced in a 

 hydrogen flame, and shows that this ratio is preserved in flames whose products of combustion contain 

 CO, and steam. The flames in these experiments were just rendered non-luminous by adjusting the air 

 supply, and the temperatures of all of them were probably pretty much the same. 



