184 Pedler — On the .Calcutta Goal- Gas. [AtiGusT:, 



power of the gas was due either to the presence of a considerable amount of 

 impurity, or to an imperfect manufacture of the gas. So far as I am aware^ 

 the composition of the gas supplied to Calcutta has never been ascertained, 

 and it appeared to me that it would be interesting to determine its exact 

 chemical composition, so as to judge of the cause of its bad quality. Foi* 

 this purpose, I have made a series of analyses, the results of which are ap- 

 pended in the table on the opposite page. In the first four columns of the 

 table will be found four analyses of the gas supplied on various days to 

 Calcutta, and in the fifth column, is given the average composition of 

 the Calcutta gas as deduced from twelve analyses. For the purposes of 

 comparison, I have introduced into the table the anatyses of two samples 

 of London gas, and one sample of Manchester gas, the latter being of good 

 quality, the two former only fair in quality. 



The illuminating power of any sample of coal-gas depends upon the 

 amount of the illuminating hydrocarbons (belonging to the Cn H211 series) 

 which it contains, and, to a great extent, on the proportion of carbon contain- 

 ed by these hydrocarbons, as shewn by the amount of carbonic acid generated 

 by them. A glance at the table will shew that in luminiferous constituents 

 the Calcutta coal-gas is tolerably rich, and yet we have .already seen that 

 the illuminating power is in fact less than that of London gas, which contains a 

 much smaller proportion of hydrocarbons ; it therefore at once becomes evident 

 that the loss of light must be due to the presence of some impurities. 



The chemical composition of the gas shews that there are both imper- 

 fections in its manufacture and in its purification. In the first place, we 

 have no less than 4*79 per cent, of carbonic acid present in the gas ; this, 

 as is well known, is an impurit}- most destructive to the illuminating power ; 

 it has been shewn that for every 2 per cent, of this substance present the 

 illuminating power of coal-gas is diminished to the extent of from one 

 candle to one and a half candles ; that is t3 say, if this impurity were 

 removed (which is a very simple matter) the illuminating power of the gas 

 would be increased from thirteen candles to about fifteen or sixteen candles. 

 The second point that I have to draw attention to, is the extremely large 

 amount of nitrogen present ; this can only arise from imperfections in 

 the manufacture ; it means to say, that about 15 per cent, of the gas 

 supplied as coal-gas, has been drawn in from the air during the process of 

 manufacture, and it shews that either the retorts are in a very dilapidated 

 condition, or that sufficient care is not taken to keep the retorts properly 

 closed, when the gas is being formed. The presence of the nitrogen in 

 the gas is decidedly detrimental to its illuminating power, but even sup- 

 posing that it has simply a diluting effect, and no injurious action on the 

 gas, the absence of the nitrogen would raise the illuminating power from 

 13 to 15 '3 candles. It haS; however, been shewn by the experiments of 



