1894.] The Action of Heat upon Etliylene. 95 



the oxides of carbon and increase on the nitrogen showing that 

 some air had remained in the tube. 



A second analysis was now made, but instead of estimating the 

 saturated hydrocarbons by first absorbing the higher members and 

 some methane by paraffin, they were exploded with oxygen, and the 

 methane calculated from the carbon dioxide amounted to 112' 5 per 

 cent., showing that ethane and probably even higher members of the 

 series were present, results which fully bear out the statement 

 made by Day as to the decomposition of the ethylene taking place at 

 a temperature of 400 C., and also the statements made by Berthelot 

 and by Day, that under the conditions of this experiment ethane or 

 at any rate higher members of the C n H 2B+2 series are formed as well 

 as methane. 



It would, however, be manifestly wrong to assume that the forma- 

 tion of the higher paraffins was a primary action, as keeping the 

 hydrocarbons formed by the primary changes at a temperature of 

 400 C. might easily lead to the formation of secondary products by 

 interaction between the gases. 



It seemed much more probable that the character of the primary 

 decompositions would be ascertained by rapidly heating the gas, and 

 as rapidly removing the products of decomposition from the influence 

 of heat, and that this would be effected by passing a regular current 

 of the gas through a very narrow tube heated for 140 mm. to a known 

 temperature. 



The necessity for heating this tube to temperatures above 1000 C. 

 practically limited the choice of material of which it could be made 

 to fire-clay or platinum. It was at first feared that the use of the 

 latter might interfere with the changes taking place, but a long 

 series of comparative experiments, in which ethylene was decomposed 

 by passing through (a) a pipe-stem glazed with borax, and (6) a 

 platinum tube 2 mm. in diameter, both being heated to the same 

 temperature, showed that the platinum tube was free from experi- 

 mental objection unless a considerable percentage of oxygen was 

 present, and that, even with a new tube, the decompositions were of 

 the same nature as when the pipe-stem was employed. 



(Jnder these conditions the platinum tube possessed so many 

 advantages over the clay pipe that in all the subsequent experiments 

 a platinum tube, 2 mm. in diameter and about 40 cm. in length, was 

 used, and, in order to accurately measure the temperature to which 

 the gas in the tube was heated, the following arrangement was 

 devised : 



Ethylene was stored in a gas-holder, and, after passing over calcic 

 chloride to dry it, entered the platinum tube. In this tube the 

 platinum and the platinum-rhodium thermo-couple was arranged in 

 the following fashion : 



