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COKTBIBUTIONS TO THE KNOWLEDGE 



retort. The water gas was produced, as usual, by allowing 

 a thin stream of water to fall upon charcoal heated to full 

 redness in a separate retort ; this gas, along with the excess 

 of steam, then passed into the lower division of the coal 

 retort, sweeping in its course the gases forming in both the 

 lower and upper divisions rapidly into the hydraulic main, 

 and producing, in its passage, an additional quantity of 

 water gas by the action of the steam upon the coal tar. The 

 production of the water gas was so regulated as to be most 

 rapid at the commencement of the experiment, and then 

 gradually to decline to its close. 



For the purification of the gases nothing more was used 

 than two small purifiers, the one containing wet and the 

 other di'Y lime ; but on the large scale, arrangements ought 

 to be made for removing ammonia as well as sulphuretted 

 hydrogen. There is, however, no constituent contained in 

 the gases made by the new process applied to coals, which 

 requires means of purification different from those commonly 

 used in all gas works. 



The samples of gases employed for testing the illuminating 

 power and for analysis, were collected in the following man- 

 ner : — The main conveying the gas from the purifiers to the 

 holder was tapped at a point just before it entered the meter, 

 and a tube attached leading to a graduated gas-holder capable 

 of containing 80 cubic feet. The flow of gas into this holder was 

 so regulated by a stop-cock as to allow the admission of a cer- 

 tain per centage throughout the entire working; for instance, 

 if a 10 per cent, sample was being taken, 10 feet entered this 

 holder during the time 90 feet passed through the meter. 

 The per centages varied from 3 to 10 in the diiferent experi- 

 ments, but they were always made as large as the size of the 

 holder rendered practicable. The volume of gas thus extracted 

 was noted, and added to the quantity indicated by the meter. 

 This method is much more convenient and accurate than 

 when a large holder is employed and the total quantity of 



