526 THE POPULAR SCIENCE MONTHLY 



tedious, to find the conditions under which the line appeared. I tried 

 filling the discharge-vessel with all the gases and vapors described in the 

 books on chemistry without success. At last I tried bombarding various 

 substances with cathode rays. Under this treatment the substances 

 give off considerable quantities of gas the greater part of which is 

 hydrogen, carbonic acid or carbon monoxide. When I came to analyze 

 by the positive rays the gases given off in this way, I found that with a 

 large number of substances these gases contained the substances giving 

 the three lines, so that I was now in a position to get this line whenever 

 I wanted it, and investigate the properties of the gas to which it owes 

 its origin. The question of the gases absorbed and given off by solids 

 is an extremely interesting one, and a considerable number of investi- 

 gations have been made on it. In all these, as far as I know, the method 

 has been to heat the solid to a high temperature, and then measure and 

 analyze the very considerable amount of gas which is driven off by the 

 heating. As far as I know, no experiments have been made in which 

 the gases were driven off by bombardment with cathode rays. This 

 treatment, however, will cause the emission of gas even when ordinary 

 heating fails to do so. 



Belloc, who has recently published 2 some interesting experiments on 

 this subject, after spending about six months in a fruitless attempt to 

 get a piece of iron in a state in which it would no longer give off gas 

 when heated, came to the conclusion that, for practical purposes, a 

 piece of iron must be regarded as an inexhaustible reservoir of gas. 

 There are some interesting features about the emission of gas from a 

 heated solid. If the body is kept for a long time in a vacuum at a high 

 temperature, the emission of gas becomes too small to be detected; if 

 after this treatment the temperature is raised considerably, there will be 

 a further copious emission of gas, which again diminishes as the heat- 

 ing continues. After it has fallen to zero, all that is necessary is to 

 raise the temperature again and you will get a fresh supply of gas ; and 

 as far as my experience goes, after you have got all the gas you can out 

 of the solid by heating it, you have only to expose it to cathode rays to 

 get a fresh outburst. This effect of increased temperature in renewing 

 the stream of gas from the solid seems to me to be too large to be ac- 

 counted for merely by an increase in the rate of diffusion of the absorbed 

 gas from the interior to the surface; it seems to be more analogous to 

 the case of the emission of the water of crystallization from some salts. 

 There are some salts, for example, copper sulphate, which when heated 

 lose their water of crystallization in stages ; -thus, if the temperature is 

 raised to a certain value, some of the water of crystallization comes off, 

 but the rest remains fixed, and you may keep the salt at this tempera- 

 ture for ever without getting rid of all the water of crystallization ; on 



2 Ann. de Chimie et cle Physique (8), XVIII., p. 569. 



