238 ANNUAL OF SCIENTIFIC DISCOVERY. 



equal to 1-90 candles; and gas No. 4, four days old, gave the light of T75 

 candles, the quantities representing the average of repeated trials. 



It thus appears that the illuminating material of our coal-gas is so rapidly 

 abstracted by suffering it to remain in contact with water, that the same vol- 

 ume of gas which to-day will give me the light of nearly 11 candles, by 

 standing until to-morrow will give the light of only 3'50 candles; and if left 

 standing four days, will give the light of only 1'75 candles; while the only 

 means left to the consumer to get the light he requires from this deteriorated 

 gas, is to bum more of it, as we have all been doing through the past winter. 

 If we now take into account the well-known fact, that gas of less illuminat- 

 ing power has less density, and that gas of less density passes more rapidly 

 through a given aperture than gas of greater density, we have another cause 

 operating to increase the consumption. In Hedley's experiments, the Argand 

 burner, which gave the light of 25 candles when supplied with three cubic 

 feet per hour of gas from Welsh cannel coal, with a specific gravity of "737, 

 required no less than seven and one-half cubic feet per hour to give the 

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

 castle 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 it 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 manifest that the 

 public are 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 manu- 

 facturer. 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, to- 

 wards the close, he allows the heat to rise a little too high, the result is inevi- 

 table, 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 we assume the last quantities to 

 represent the value of the gas when 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 quality established by the 

 proper authorities, taking the illuminating power as the basis of the calcula- 

 tion, and then to have the requirements 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, hydro- 

 gen and light carburretted hydrogen, that make up the bulk of the ordinary 

 coal-gas. 





