19? On Oil and Coal Ga&^ [S e pt. 



observed the empyreuma alone ; but frequently the other is per- 

 ceptible also, and sometimes it prevails to an insufferable 

 degree. 



The most serious objection to coal gas arisefe from the pre- 

 sence of impurities. These are, a black matter like tar, and 

 compounds of sulphur, — all derived from the coal itself, and 

 therefore necessarily present originally in every description of 

 coal gas. Without purification, therefore, coal gas could scarcely 

 be used at all ; and it becomes a question of importance to deter- 

 mine, whether or not the noxious ingredients may be wholly 

 removed from it. The greater part of the tar is deposited at the 

 works in the proper vessels, but a minute portion does com- 

 monly pass over with the gas. It tends to clog the apertures of 

 the burner, and of course soils substances upon which it is depo- 

 sited. In common shops, where a free current of air is pre- 

 served, the effect is hardly noticed ; but we suspect that a part 

 of the inconvenience found by jewellers to attend the use of coal 

 gas arises from this cause. 



The most formidable of the compounds of sulphur present in 

 coal gas is sulphuretted hydrogen. The presence of this gas is 

 hurtful in two ways. If it escape unburnt, it offends by its 

 insupportable odour, and attacks silver, and paint, with great 

 readmess. When consumed, it forms sulphurous and sulphuric 

 acids, which may injure the health, if habitually inspired, and 

 act chemically on various substances, as on iron and steel. 

 Hence the necessity of removing it entirely from coal gas. On 

 this subject two important questions naturally occur, to both of 

 which we can give a decisive answer. 1st, Can sulphuretted 

 hydrogen be wholly separated from coal gas ? and, 2dly, when 

 it is removed. Can coal gas be regarded as perfectly free of 

 sulphur ? 



We are satisfied that sulphuretted hydrogen may be wholly 

 removed ; for we have repeatedly examined the Edmburgh coal 

 gas by the most dehcate tests, without detecting a trace of it. 

 Of course we do not vouch that it is always equally pure, be- 

 cause the least neglect, on the part of the workmen, must inevi- 

 tably cause some sulphuretted hydrogen to escape into the 

 pipes. It is equally certain, however, that coal gas, when com- 

 pletely free of sulphuretted hydrogen, still contains sulphur. 

 On burning a small jet of coal gas, free from sulphuretted hydro- 

 gen, so as to collect the fluid formed during the combustion, 

 the presence of sulphuric acid was uniformly detected, demon- 

 strating the existence of some compound of sulphur. What 

 that compound is has not yet been ascertained ; out from its 

 pecuHar unpleasant odour, and the circumstances under which 

 It is generated, the sulphur is most probably in combination 

 with carbon, either in the form of the volatileliquid, sulphured 



