Parrot Coal for yielding Gas. 225 



In obtaining gas from the coals, the composition of which 

 has been given, I employed an apparatus erected in my labo- 

 ratory for the purpose, and constructed in the usual way. 

 The retort was capable of being charged with 5 lb. of coal. 

 The condenser consisted merely of a system of pipes, of nearly 

 100 feet in length, and two inches internal diameter. The 

 purifier contained three shelves with dry slaked lime, by which 

 the gas was thoroughly purified before going into the gasome- 

 ter. In the different trials, the quantity of coal used was the 

 same in all, viz. 5 lb. ; and the temperature, to which the re- 

 tort was brought, was, as nearly as could be judged of by 

 its appearance, also the same in all. The time for taking off 

 the gas, of course varied in the different cases ; in general, it 

 was from 50 to 60 minutes. 



Different methods were had recourse to for ascertaining the 

 illuminating power : 1*/, The shadow. For this purpose, a 

 wax candle, burning as nearly as possible with the same flame, 

 was contrasted, at different distances, with a single jet of 5 

 inches, using the same jet in all the trials. 2g?, The condensa- 

 tion by chlorine, following the method described in my former 

 paper. These are the tests in which I place the most con- 

 fidence. 3fl?, The time required for the consumpt of a given 

 quantity. In the trials, a single jet of 5-inch flame, always un- 

 der the same pressure, was used. 4/^, The specific gravity, 

 which was taken by Crosley's apparatus, bth. The length of 

 flame from a single jet, under a pressure of one inch. This 

 last is what is called Aldcock's burner. 



In conducting these trials, due attention was paid to every 

 circumstance, so as to secure accuracy in the results, not only 

 in the manufacture of the gases, but also in ascertaining the 

 illuminating power by the methods above mentioned. For the 

 sake of brevity, the results are given in a tabular view. 



