﻿Ignition of Gases by Sudden Compression. 115 



the true value, even when all possible sources of error are 

 taken fully into account. 



XVII. It has already been mentioned that when the time 

 of ignition by compression of hydrocarbons (and of ether) is 

 small, i. e. when the gases are suddenly compressed to a 

 temperature well above the ignition temperature, carbon is 

 thrown down, even though excess of oxygen is present. In 

 the experiments with CS 2 an even more curious phenomenon 

 was noticed. In this case, whereas the sulphur burns to 

 S0 2 when the initial temperature of compression does not 

 exceed very greatly the lowest ignition temperature, when 

 the initial temperature is high the products of combustion 

 smell strongly of JBLS. For instance, the products of com- 

 bustion in experiments E x and E n above both smelt strongly 

 of H 2 S, although in E 2 -E ]0 inclusive only S0 2 could be 

 detected by smell. It was also possible to detect H 2 S after 

 experiments F 6 and F 10 (with the fan), the smell being 

 particularly strong in the case of F 10 . The smell of H 2 S 

 could also just be detected along with S0 2 in experiment F 9 , 

 whereas in the remainder only S0 2 could be detected. 



The H 2 S could only have come by combination with w r ater- 

 vapour present in the air, which was not dried. This 

 occurrence of H 2 S is all the more interesting since it is 

 known that a perfectly dry mixture of CS 2 and oxygen can 

 be exploded by a spark, whereas perfectly dry mixtures of 

 other gases, e. g. carbon monoxide with oxygen, cannot. It 

 is possible that some such reaction as 



CS 3 + 2H s O = CO s + 2H s S 



takes place, followed by the combustion of H 2 S ; but even if 

 this is the case, it would be expected that the H 2 S would be 

 quickly burnt in presence of excess of oxygen under the 

 conditions of these experiments. Further experiments on 

 the ignition of H 2 S itself will probably throw some light on 

 these observations. 



XVIII. In Table XVIII. are summarized the chief results 

 of the experiments described above. The ignition tempera- 

 tures represent the lowest average temperatures at which 

 the non-turbulent mixture could be caused to ignite. The 

 rates of evolution of heat at these temperatures for the three 

 cases are calculated from the cooling factors and the specific 

 heats of the mixtures. 



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