236 ANNUAL OF SCIENTIFIC DISCOVERY. 



in close vessels contains hardly any illuminating material. At that tem- 

 perature it is furnished most freely, but after having been formed, is liable 

 to decomposition, involving a loss of carbon by contact with any highly 

 heated surface, in passing through the apparatus, such decarbonization 

 increasing with the degree of heat, with the extension of the red-hot sur- 

 face, and with the time of contact. Again, the duration of heat is most 

 important, the best gas coming over during the first hour, the quality rapidly 

 deteriorating, until, at the expiration of four hours, the product is worth 

 very little to the consumer, and after five hours may be considered as worth- 

 less. But the bulk of such worthless gas that can still be obtained by push- 

 ing the process to completion, is very considerable, equal sometimes to 

 two-fifths of all that passes over. 



How far any neglect in the observance of the precautions required to pro- 

 duce a proper illuminating gas, may explain the result, the public have no 

 means of knowing. All that we know is, that the manufacturers furnish an 

 article which they say is the right article, and prepared in the right way, and 

 possessing an illuminating power varying from fourteen to seventeen candles. 

 That is, their engineer reports, that on trial with a photometer, at stated 

 times, the gas burning from a jet, consuming five cubic feet per hour, gives 

 an amount of light equal in the average to that of fifteen patent candles, six 

 to the pound, the patent candle being ostensibly a mixture of spermaceti 

 and wax. Assuming as true all that is claimed by the manufacturers, it can 

 still be shown that the gas, even if properly made and correctly tested, may 

 be, and is, furnished to the consumer in a condition of greatly diminished 

 illuminating power, compelling the consumption of a greater bulk to obtain 

 the required light, and consequently swelling the record of the meter and 

 the sum-total of the quarterly bills. In my trials to determine the specific 

 gravity of our gas by weighing a globe previously exhausted and then filled 

 with it, I obtained a result ranging from '570 to '580, somewhat below that 

 given as characterizing good gas. But in reality I attach very little impor- 

 tance to this result, since the mere specific gravity of such a complex 

 mixture as coal-gas, can hardly be relied upon to determine its commercial 

 value. 



Although good gas certainly has a higher specific gravity than poor, yet 

 the difference could not be taken to represent the true difference in value, 

 since the principal components of the mixture hydrogen, carbonic ox- 

 ide, light carburretted hydrogen, olefiant gas, and other still heavier hydro- 

 carbons having specific gravities widely different might vary somewhat 

 in their relative proportions, sufficient to affect the illuminating power, 

 without at the same time, and to the same extent, affecting the specific 

 gravity. The action of chlorine in removing the olefiant gas, and other 

 more dense hydrocarbons, the principal light-giving materials of the coal- 

 gas, showed a percentage of these substances never exceeding ten per cent. 

 But, not having time at the moment to guard against all sources of error in 

 the process, I laid it aside. My attention was principally directed to the 

 simple inquiry, To what extent will the illuminating power of the gas be 

 impaired by keeping it in contact with water for noted periods ? That it does 

 deteriorate when thus kept, or when kept in contact with oil, or even close 

 vessels, has been long known. 



Dr. Ure tells us that gas from oil, when first made, and with a specific 

 gravity of T054, will give the light of one candle, when burned from jets 

 consuming 200 cubic inches per hour. But keep the gas three weeks, and 



