432 PROCEEDINGS OF THE AMERICAN ACADEMY. 



which an electrical current was passed. The assumption that must be 

 made with regard to the partial pressure of the carbon monoxide is 

 that it is constant and is due to oxygen of the air acting on the carbon 

 tube, giving one-third of an atmosphere. 5 Unless the temperature is 

 raised above that corresponding to one-third of an atmosphere, no car- 

 bide would be found. By repeated trials this temperature could be 

 located within certain limits, if the above assumption is true. In this 

 way Rothmund found 1620° C. as the temperature of formation. Sim- 

 ilar experiments were repeated later by Rudolphi, 6 who found the tem- 

 perature of formation to lie between 1800 and 1819° C, that is, about 

 200° higher than Rothmund's value. The temperature measurements 

 were made by an optical method, as were also Rothmund's. Finally, 

 Lampen, 7 by a method similar to the above, using a Wanner pyrometer 

 for temperature measurements, found 1725° C. for the temperature of 

 formation. It seemed evident, from the poor agreement of these results, 

 all obtained by the same method, that some other method would have 

 to be used in which the pressure of the carbon monoxide could also be 

 measured, as these differences might be due simply to different values 

 of this quantity. It was the object of the following investigation to 

 make these measurements. 



2. Method and Results. 



The method decided on was to heat the charge in a vacuum furnace 

 connected with a mercury manometer and to measure the temperature 

 of the charge and pressure of the carbon monoxide when equilibrium is 

 reached. A small Arsem 8 vacuum furnace, made by the General Elec- 

 tric Company, was the apparatus used. It consists of a cylindrical ' 

 bronze casting 24 centimeters in inside diameter and 39 centimeters in 

 length. Parallel to the axis in the center of the casting and fastened 

 to the lid, is a graphite helix, 27 centimeters in length, 5.1 in outside 

 diameter and 0.5 in thickness of wall. The helix is clamped at each 

 end by water-cooled electrodes. The lid is fastened to the casting with 

 a number of cap-screws and a lead washer. The whole furnace is im- 

 mersed in water with the exception of a tower projecting from the center 



6 Rothmund erroneously assumes the pressure of the carbon monoxide to 

 be 1/5 atmosphere, probably because this is the partial pressure of oxygen in 

 the atmosphere. Taking into consideration that every mole of oxygen pro- 

 duces two of carbon monoxide, 1/3 atmosphere is the result obtained. 



6 Zeitschr. f. anorg. Chem. 1907, 54, 170. 



7 Jour. Am. Chem. Soc, 1906, 28, 864. 



8 Trans. Am. Electrochem. Soc, 1906, 9, 163. 



