192 TRANSACTIONS OF THE 



that is, cleaning the retort, by the admission of atmospheric air 

 to burn out the residuum arising from the decomposition of the 

 oil. His method, and whicli he still uses, was to admit air by 

 simply raising one side of the cover a little, whenever the clean- 

 ing was requisite, and opening at the same time a communication 

 from the interior of the retort to the chimney, whereby a draft 

 was obtained. The air so admitted caused a direct combustion of 

 the residuum. The products of this mainly pass off into the 

 chimney, a slight deposit only being left on the bottom and sides 

 of the retort, in the form of ashes, and this is not sutficient in 

 quantity to require removal oftener than once in three or four 

 weeks. 



The committee do not understand that the method of effecting 

 the same purpose, as now exhibited by the Maryland company, 

 possesses any advantage over that of Mr. Coates. It is certainly 

 not so manageable by the class of operatives by whom these port- 

 able generators are professedly to be worked. If introduced into 

 the large gas manufactories where the D retort is altogether used, 

 their method probably would be the one selected, but in the 

 "portable work," as they are called, the cauldron shaped retort 

 has been generally, and for good reasons, preferred; and it is with 

 these only we have to do at present. The apparatus of Mr. Coates 

 has this year another and a marked improvement, being that in 

 which it is, as before remarked, dilferent from his exhibition at 

 our fair in 1856. This lies in casting the retort uniformly thin 

 throughout its entire body, and then obtaining the thickness of 

 bottom requisite for insuring equality and steadiness of heat, by 

 putting in a quantity of lead. This is soon melted, forming a 

 level surface; and as upon this it is well known that the oil is 

 not so readily decomposed as upon iron, he places a plate of that 

 metal upon the lead, where of course it floats. By this arrange- 

 ment, the retort being of equal thickness throughout, is (1) not 

 liable to be cracked in getting up a heat; (2), if the bottom sags, 

 as from the heat it is apt to, the lead and plate of iron upon it 

 still preserves the necessary form of surface requisite to insure 

 the proper distribution of the oil; and, (3), the only part which 

 wears out rapidly, viz, the iron upon which the decomposition is 

 effected, may be cheaply replaced. 



