EXPLOSIONS OF COAL-GAS AND AIR. 370 



to 0*008 gr. of water per sq. cm., to an absorption of heat of 0'0109 calories 

 per sq. cm. 



In order to apply a correction for the loss of heat by the bolometer as it warms up 

 the record was continued for some time after the radiation from the gas was 

 inappreciable.* From the rate at which the galvanometer deflection decreased the 

 rate of loss of heat by the bolometer was determined. In this way it was found that 

 in this particular record the loss amounted to 6'1 per cent, of the heat in the 

 Ixilometer at 0'5 second after ignition, and 13'5 per cent, at 1 second after ignition. 



RESULTS OF EXPERIMENTS. PART I. 



The following radiation measurements were made in explosions of mixtures of 

 Cambridge coal-gas and air of various strengths and densities. Measurements of the 

 radiation received by the walls per sq. cm. of surface were made at three different 

 places on one of the end covers, A, B, and C, as shown in fig. \b. The amounts 

 measured in the three places were distinctly different and showed peculiarities which 

 will be discussed later. In all the experiments about to be described in this section 

 the interior surface of the explosion vessel was painted over with a thin layer of dull 

 black paint, so that practically all the radiation emitted by the gas was absorbed by 

 the walls, t 



Two or three records were generally taken under the same conditions ; those taken 

 on the same day gave precisely the same results. 



Mixtures of Various Strengths fit Atmospheric Density. 



The results shown in figs. 4-11 refer to experiments made with the fluorite window. 

 An allowance of 5 per cent, has been made for the absorption of the fluorite,| but no 

 allowance has been made for reflection from tin- blackened surface of the bolometer. 

 The curves in these figures, therefore, show the radiation <d>surl><'<l by the blackened 

 walls. 



Kig. 4 shows the amount of radiation received by the walls, in calories per sq. cm. 



1 This part of the record has been painted out in the print shown in fig. 3. All measurements refer to 

 the original film. The reproduction is approximately five-eighths of the original. 



t The alisorliing power of a surface painted with this black paint was compared with that of one which 

 had been blackened with camphor smoke and was found to be the same. FKRY'S experiments show that 

 a smoke-black surface would reflect about 5 per cent, of the radiation emit led by the hot gaseous mixture 

 which is of wave-length )>etween 2/i and Bji. 



I A clear plate of fluorite, from 5 mm. to 10 mm. thick, transmits very approximately 95 per cent, of 

 incident radiation up to 8/i. This figure was checked in the following way : The radiation was measured 

 when the window consisted of a quartz plate only, and also when the plate of fluorite was placed in front 

 of the quartz in explosions of identical mixtures. In the latter case the radiation measured was almost 

 exactly 95 per cent, of that in the former case. There is very little energy in the emitted radiation of 

 wave-length greater than 8/1. 



302 



