INVESTIGATION WITH A ROCK-SALT PRISM. 45 



Ethylene. C2H4. 

 (Cell, 5.7 cm. ; barom., 73.8 cm. ; temp., 22°. 5 ; fig. 14. J 



This gas was prepared from ethylenebromide, CaH^Brj (from Drs. 

 Bender and Hobein, boiling at the theoretical temperature of 131°), by 

 using a zinc-copper couple/ and was dried by passing it through a glass 

 tube containing P2O5 and absorbent cotton, to present a large surface. 



In the preliminary examination the gas showed ether bands. The 

 ethylene bromide was then redistilled, and a second examination was 

 made, the gas having been passed through a tube placed in CO2 snow. 

 After the liquid-air apparatus was set up, this gas was dried in P2O5, 

 then fractionally liquefied in bulb (/(fig. 9), kept at — 97°, and the 

 remainder liquefied in bulb e, kept at — 120°. These were the readings 

 of the petroleum thermometers, which, although constant and in contact 

 with the liquefaction bulbs, may not have been at the same temperature, 

 since they presented a smaller surface to the evaporating air. 



In the first bulb there was a liquid having a strong odor of CoH^Brg. 

 In the second tube were about 5 cc. of liquid ethylene, having a sweet 

 odor much like that of C2H4Br2, somewhat sharper, like pure acetylene. 

 It burned with a beautiful yellowish- white flame. The second frac- 

 tional distillate was used in this examination. 



The transmission curves for these three samples of gas, differently 

 prepared, showed but slight variation in the intensity and position of the 

 transmission minima, excepting that the ether band found at 7.8 \x. in 

 the first sample was absent in the others. 



That the gas was very pure is shown from the analysis by absorption, 

 using bromine water. The quantity of unabsorbed gas was so small 

 that it could not be measured accurately. 



Amount of C2H4 taken 50. 2 cc. 



Unabsorbed gas 0.6 cc. 



Total C8H4 49.6 cc. 



Purity 98.8 per cent. 



A combustion analysis, made by Mr. R. C. Snowden, of the first frac- 

 tion distilled, showed considerable impurity. From general experience 

 it appears that this is due to the method of analysis rather than to any 

 real impurity. 



The transmission of ethylene is entirely different from acetylene, 

 from which it differs in composition in having two more H atoms. It 

 is also different from CH., in which there is one less C atom. 



^A zinc-copper couple is made by placing pure granulated zinc in a dilute solution 

 of CuSOi, when the zinc becomes covered with copper. When this couple is placed 

 in the liquid it immediately decomposes it. 



