33 



of hydrogen at 422 Fahr., leading to the hope that here was a com- 

 pound of definite composition which would admit of correct analysis 

 and perhaps of formulation ; but some more of the naphthalin, pro- 

 duced, like the other, from Newcastle coal, but at another gas-works, 

 possessed such diifererit physical properties as to convince me that 

 very much more must be known of this substance before any reliable 

 analyses can be published. The latter sample gave a neutral solu- 

 tion in spirit, like the other, but of a considerably browner colour. 

 When heated alone it gave off ammonia with ebullition at 2 18 Fahr., 

 and then became tranquil. When the temperature reached 375 

 Fahr., it began to evolve sulphide of hydrogen, which continued to 

 increase in quantity up to 390 Fahr., when it nearly ceased, and 

 quite ceased at 4 10 Fahr. The proportion of tar in this sample was 

 much greater than I have seen it in any other. Subsequently I 

 obtained some more naphthalin which had been deposited in the 

 pipes of another London gas-works, and this, like the former, con- 

 tained both nitrogen and sulphur, which were evolved upon distil- 

 lation as sulphide of hydrogen and ammonia. 



Having thus obtained one sulphurized hydrocarbon, and deter- 

 mined the temperature at which its sulphur and nitrogen could be 

 obtained as easily removeable compounds, I was prepared to advance 

 towards a better purification of gas with great probability of success. 

 Another well-confirmed observation helped to guide me. Gas freed 

 from every trace of sulphide of hydrogen always blackens lead-paper 

 strongly when passed through clay ; and if it be subsequently passed 

 through lime, it affects turmeric though quite free from ammonia 

 when taken for experiment. This process may be repeated through 

 a series of ten or twelve purifiers containing clay and lime placed 

 alternately, the test-papers being less affected at each purifier, until 

 at length they are riot discoloured at all. This experiment has been 

 made upon gas produced in various parts of England and Scotland 

 from many kinds of coal, and I think the number of instances suf- 

 ficient to justify the conclusion that all gas, as sold, contains the 

 compound from which clay liberates sulphide of hydrogen. I have 

 not yet been able to separate the compound upon which clay 

 thus acts. I have, however, ascertained that the clay which has 

 liberated sulphide of hydrogen from gas which did not affect test- 

 papers when taken for experiment contains tar, which may be dis- 



VOL. XI. D 



