PLATINUM SURFACE AT HIGH TEMPERATURES. 
247 
At increasing pressures the decomposition became more rapid, and finally, in an 
experiment in which the apparatus had, at the start, been partially filled with 
liquid gas, it took the form of a sharp explosion. The temperature of decomposi¬ 
tion is for all pressures about the same, and lies between 800 and 900 degrees 
Centigrade. 
Some measurements taken in liquid nitrous oxide and liquid carbon dioxide are 
given in Table VII. (p. 251). 
Conclusions. 
The general result of the investigation is to show that the law which connects the 
thermal emissivity with the temperature of the radiator and the jDressure of the 
gas is— 
E = 
where E = Emissivity = Heat dissipated per second, per degree Centigrade tempera¬ 
ture interval, per centimetre of area, expressed in gramme-degrees, a, a, 6, ,5, are 
the constants given on page 236, ]o is the pressure in atmospheres, and d the 
temperature interval. 
The hearing on astro-j^hysical problems is at once apparent, and the high effective 
conductivity of compressed gases must be taken into account when treating questions 
relative to the mean temperature of the sun, its rate of cooling, or more generally, 
any problem dealing with the physical state of gaseous astral bodies. 
Although extrapolations are always very uncertain, in the present case it seems 
justifiable to conclude that under the very great pressures with which astronomical 
physics has to deal, all gases or vapours would transmit heat at a higher rate than 
the best conducting solids known. 
From a practical point of view, the results obtained explain the very rapid cooling 
of the products of an explosion, a fact which has not ordy l)een noticed during the 
course of experiments on ballistics, but has long been well known to all engineers 
engaged in the construction of gas engines. 
The relatively small cooling surface required, in the case of gases under high 
pressures, is a fact that had been previously noticed, and is already to some extent 
taken account of in the design of the modern compressors. 
The laws of thermo-dynamics show that the efficiency of all lieat engines is 
dependent on their temperature range and pressure : in compliance with these laws 
the pressures used are daily becoming greater. It is therefore hoped that the present 
investigation may be of some use to those engaged in practical engineering. 
Before closing, I desire to express my indebtedness to Dr. Ludwig Mond, the 
donor of the Davy-Faraday Laboratory, at which Institution the greater part of the 
work was carried out. My sincere thanks are also due to Dr. Alexandee Scott for 
the kind way in which he has facilitated the research by every means in his power. 
