140 Variable Illuminating Poiver of Coal Gas. 



737, required no less than 7^ cubic feet per hour to give the same 

 light, from the same burner, when the gas was made from the 

 Newcastle coal and had a specific gravity of only 475. 



Again, as we diminish the illuminating power of the gas we 

 increase its heating power, and this necessarily brings with a 

 higher temperature given to the burners, a higher temperature 

 given to the gas passing through them, and again an increased 

 rapidity in the flow. It is thus manifested that the public 

 placed in a peculiarly unfortunate position, since all the mistakes 

 that are likely to occur in the process of manufacture are mistakes 

 that must inevitably increase the bills of the consumer and the 

 profits of the manufacturer. If the workman fails to raise the 

 heat with proper rapidity, if he overlooks a retort and allows the 

 heat to continue a little too long, if towards the close he allows 

 the heat to rise a little too high, the result is inevitable, the product 

 is deficient in illuminating power. Or if on any one day a little 

 more gas is produced than is legitimately required, the surplus 

 remains in the gasometer to vitiate the supply of to-morrow\ To 

 what extent this vitiating action operates may be inferred from 

 the fact that I have never been able to obtain from the gas of our 

 pipes an illuminating power equal to the minimum of that reported 

 by the engineer of the gas company. In my trials the power has 

 varied from that of 13 candles down as low as that of 9 candles, 

 instead of ranging from 14 to 17 candles. 



This difference is perfectly intelligible if w r e assume the last 

 quantities to represent the value of the gas w r hen first made, and 

 my results to represent its value as delivered to the consumer. 



In conclusion I would merely add that the difficulty suggests 

 its own remedy. And that would be to have a standard of qua- 

 lity established by the proper authorities, taking the illuminating 

 power as the basis of the calculation, and then to have the require- 

 ments of such standard insured by a nightly examination, if 

 necessary on the part of some one entirely disconnected with the 

 manufacture. In other words the photometer can be made as 

 available and as valuable to the consumer of gas as the hydrometer 

 is to the spirit merchant; as he distinguishes with his instrument 

 in any mixture, between the spirit he wishes to buy and the water 

 he is unwilling to pay for, so the consumer of gas can distinguish 

 with the photometer between the true illuminating material and 

 the worthless heat producing gases, hydrogen and lihtg curburet- 

 ted hydrogen, that make up the bulk the ordinary coal gas. 



