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feet of gas, and the use of many thousand tons of the refuse as ma- 

 nure, I venture, for the first time, to submit the grounds upon which 

 my process is based. 



Coal-gas may conveniently be considered under the heads of carbon 

 compounds required for the production of heat and light, which 

 generate water and carbonic acid by their combustion ; and sulphur 

 and nitrogen compounds which are not necessary for heat and light, 

 and ought to be removed from gas on account of the injurious nature 

 of the substances produced by their combustion. 



The former of these classes will be treated of incidentally ; the 

 latter class forms the principal subject of this paper. When speaking 

 of gas, I always refer to that which has undergone the ordinary con- 

 densation of gas-works, wherefore no mention is made of the complex 

 compounds removed by condensation. 



When coal is distilled, its nitrogen is evolved in some forms of 

 combination which are generally familiar, while others are almost 

 unsuspected. Under certain conditions of distillation, much nitrogen 

 leaves the retorts and passes the condenser as ammonia or some of 

 its salts. These are all removed from gas by clay, so that no trace 

 of ammonia can be discovered after gas has passed through purifiers 

 charged with an adequate quantity of clay, and with lime or some 

 equivalent substance to remove sulphide of hydrogen. Clay is thus 

 entitled to be classed with acids and some metallic salts as a purifier 

 of gas, for these, of course, remove ammonia and its salts. But 

 between clay and acids there is an important difference, in regard to 

 the action which takes place upon the most valuable light-giving con- 

 stituents of the gas ; acids remove a large quantity of these, clay 

 does not. We have experimental proof that clay does not remove 

 the valuable hydrocarbon vapours from gas, in the fact that strong 

 spirit of wine digested upon foul clay for days, does not thereby be- 

 come much more luminous than it was before being so treated. 

 The very slight light-giving power which it has obtained is due to 

 tar ; for if the spirit be evaporated, and the tar so obtained be redis- 

 solved in fresh spirit, the same kind of flame will be obtained as 

 before ; whereas the addition of a small portion of coal-oil to spirit 

 gives a flame of considerable illuminating power. To this I may add, 

 that long and extensive experience shows that the employment of clay 

 in the purifying process improves the light-giving power of gas, by 



