324 Mixter — Experiments with Endothermic Gases. 



was a thick wrapping of cotton wicking to protect the rubber 

 stopper from the wire used to hold it in place. Such a connec- 

 tion answered for a pressure of 20 atmospheres by the pump 

 and withstood explosions that burst the other limb of the II- 

 tube. For filling the apparatns a little mercury was poured in 

 to form a trap at the bend and the air was displaced by passing 

 in a liter or more of gas through a small rubber tube reaching 

 to the closed end ; then more mercury was added, the stopper 

 adjusted, the apparatus placed in a tall glass jar to prevent 

 danger from flying glass and to catch the mercury in case the 

 tube broke. The desired pressure was obtained by forcing in 

 water with a pump. For pressures of three atmospheres or less 

 a reservoir of mercury connected by means of a rubber tube 

 was convenient, the heigh th of the mercury in the reservoir 

 above its surface 'in the U-tube being the measure of the pres- 

 sure. For heating gases by a glowing wire the end with the 

 electrodes in fig. 1 was modified as indicated in fig. 2. To the 

 heavy copper wires passing through the rubber stopper was 

 soldered a platinum wire which was made to glow or even 

 melt by a battery current. 



Acetylene. 



Berthellot and Vieille* have investigated the explosion of 

 acetylene, and hence it is only necessary to state 

 that -my results, obtained before their paper was 

 published, accord with theirs and that they are 

 briefly given in order to show that the other 

 endothermic gases tested do not explode in the 

 same apparatus and under the same conditions. 

 At a pressure of two atmospheres when an elec- 

 tric spark was passed or a platinum wire was made 

 to glow in the gas it sometimes did not explode, 

 while at a pressure of three or more atmospheres 

 explosions always occurred. If, however, the 

 sparks are small acetylene does not explode even 

 at high pressures. A number of tests were made 

 in a tube shown in part in fig. 3, containing acet- 

 ylene under various pressures up to 20 atmos- 

 pheres ; when the inner and outer wires were 

 connected with an induction coil in action, sparks 

 visible in strong daylight passed between the glass 

 and the inner wire. This form of discharge did 

 not cause explosion.. When it continued for some 

 time a reddish deposit appeared. This was insol- 

 uble in ordinary solvents, and exploded when heated, leaving a 

 black residue. It was not further investigated. The presence 



*Compt. Read., cxxiii, 523. 



3. 



