ON GASHOUS EXPLOSIONS. 961 
The Measurement of Temperature. 
(1) Dissociation.—In the first Report the importance of dissociation 
in connection with the gas scale of temperatures, which is the only 
scale at present available for explosion and gas-engine experiments, was 
pointed out, and a hope was expressed that an investigation of dissocia- 
tion from this point of view might be undertaken by the National 
Physical Laboratory. The Committee are glad to be able to report that 
Dr. Glazebrook has given his sanction to such an investigation, which 
is now being carried on under the immediate superintendence of Dr. 
Harker, and that Dr. Glazebrook has shown his personal interest in 
this and the other matters engaging the attention of the Committee by 
joining them as a member. 
The main object of the high temperature research work which is now 
in progress at the National Physical Laboratory is to obtain direct gas 
thermometer measurements up to 1700° C. or 18009 C., and it is to this 
object that Dr. Harker’s efforts are being directed. On this inquiry 
the question as to the amount of dissociation present in the measuring 
gas has an important bearing, and may properly be included in high 
temperature research. 
In order to have the facts in a form for discussion, Dr. Harker 
prepared a Note on the early work of dissociation, particularly the 
experiments of Grove and of Deville. This Note, No. 9, in view of 
its historical interest and its bearing on their work, the Committee have 
printed in full as Appendix B. 
In view of the discrepancy which is apparent from the account given 
in this Appendix between the statements of Deville, on the one hand, 
and the recent work by Nernst and Wartenberg (which has been con- 
firmed by Holt on the other, as to the actual amount of dissociation in 
steam, CO and CO., particularly at low temperatures, it seemed of 
interest to ascertain if light might not be thrown on the question by a 
simple repetition of one or two of Deville’s fundamental experiments. 
Apparatus for this purpose has therefore been set up at the National 
Physical Laboratory, and was shown to the Committee on the occasion 
of their recent meeting at the Laboratory by invitation of Dr. Glaze- 
brook. The methods and apparatus for the purification and heat treat- 
ment of the materials used in the preparation of very refractory vessels 
were also explained. 
Sir William Preece was especially impressed with the necessity of 
repeating this early work, and accordingly the Committee welcome the 
installation of Deville’s experiments under modern conditions and with 
modern appliances for the accurate measurement of temperature which 
were unavailable in Deville’s time.? 
(2) Measurement of Pressure.—It was pointed out in the first Report 
that the determination of the energy function depended upon the 
measurement of the temperature of the gas experimented with, and that 
two methods had been used. According to one method, the gases them- 
selves which are within the engine cylinder or the explosion vessel are 
utilised as the thermometric fluid, and according to the other method the 
* Phil. Mag., May 1909. 
2 Professors Smithells and Bone doubt the relevance of experiments according 
to Deville’s methods to the question of flame temperature, although they welcome 
the proposed experiments from the purely scientific point of view. 
