266 Sir James Dewar [Jan. 20, 



vapour, the following apparatus (Fig. 7) was devised. A discharge 

 tube C, 3 ft. long and 2 in. diam., provided with outside tinfoil 

 electrodes, is highly exhausted by a charcoal bulb in liquid air, 

 so that no electric discharge will pass. A small carbon disulphide 

 reservoir cooled to —80° C. in soUd carbonic acid is also connected 

 to the discharge tube through the stopcock. When this stopcock 

 is momentarily turned on, the tube is charged with carbon di- 

 sulphide vapour at about 1 mm. pressure, and the discharge is 

 of a uniform lilac colour. This, however, rapidly diminishes in 

 intensity, and in a few minutes ceases, showing that a high 

 vacuum has been produced. The carbon disulphide is dissociated by 

 the electric discharge into sulphur and carbon monosulphide, the 

 latter rapidly polymerizing to a non-volatile form at the room tempera- 

 ture, as evinced by a brown stain produced on the interior surface 

 of the tube. 



Another method of detecting this monosulphide is shown in 

 Fig. 8, where a litre bulb H containing carbon disulphide vapour 

 that has been subjected to the electric discharge can be cooled 

 locally by means of a pad of cotton wool saturated in liquid air, 

 and thus any condensable material obtained as a deposit on the 

 interior of the bulb. Before the discharge is turned on, the carbon 

 disulphide distilling through the apparatus may be deposited by this 

 local cooling as a white spot which volatilizes on warming, leaving no 

 residuary mark. After the discharge is started the patch obtained in 

 this way is yellow, changing quickly to dark brown on removal of the 

 cooUng pad, it does not volatilize on warming, but leaves a permanent 

 brown film. The evanescent character of the body thus produced 

 may be seen by stopping the discharge and leaving the tube for a 

 few minutes fully charged with carbon disulphide vapour as it was 

 before the local cooling. When the pad is again applied nothing 

 but the white carbon disulphide can be condensed, and no brown 

 film results. 



The actual isolation of the volatile unstable monosulphide can 

 be accomplished in the following way. The apparatus (Fig. 8), 

 consists of a tube B containing carbon disulphide placed in a Dewar 

 vessel filled with a paste of solid carbon dioxide and alcohol, com- 

 municating through a tap C with the annular space of the ozoniser 

 A, the carbon disulphide thus giving ofiF vapour at a pressure of 

 0-8 mm. of mercury, which has proved most suitable for the passage 

 of the electric discharge to effect decomposition of the disulphide 

 into the monosulphide. The resulting gas is passed through an 

 exhausted U-tube L, a few millimetres in diameter, placed in liquid 

 air. A little above the level of the liquid air a brown ring con- 

 denses in the U-tube. This is the real monosulphide. When the 

 liquid-air vessel is removed the tube explodes, and the fragments 

 of glass are found to be partly covered with a brown powder 

 consisting of the polymerized monosulphide. It would appear that 



