1 38 Variable Illuminating' Power of Coal Gas. 



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

 specific gravity of 1*054 will give the light of one candle when 

 burned from jets consuming 200 cubic inches per hour. But keep 

 the gas three weeks and then to get the same light from the 

 same burner you must supply 600 cubic inches per hour. lie 

 adds that with coal gas the deterioration appears to be more rapid. 

 For if such gas when first made will give the light of one candle by 

 the consumption of 400 cubic inches per hour, when kept four 

 days will require the consumption of 460 cubic inches per hour 

 to give the same light. My first attempt to obtain some definite 

 results began on the evening of the 8th ultimo, when I filled a 

 a large receiver from the street main and placed it on the shelf 

 of the pneumatic trough, the next evening I filled a second one 

 and put it alongside of the first, the following evening I filled a 

 third receiver, and still the following evening, the 11th inst., I 

 filled a fourth receiver. On the evening of the 12th I was thus 

 provided with four jars of gas, one of which had been standing 

 24 hours or one day over the pneumatie trough, this I will call 

 No. 1 ; another, No. 2, had been standing two days ; No 3 had 

 been standing three days, and No. 4 had been four days in con- 

 tact with the water. The diminution in volume by such exposure 

 was indicated by a receiver graduated to cubic inches into which 

 I introduced 130 cubic inches of gas on the evening of the 8th; 

 on the evening of the 12th this had lost about 10.^ cubic inches, 

 indicating a loss of about 8 per cent, of the original bulk. 



The effect produced on the illuminating power of the gas by 

 the loss of volume became at once apparent as I proceeded to 

 contrast the value of the flames furnished by the contents of the 

 several receivers, 1, 2, 3, and 4. I used for this purpose the or- 

 dinary photometer arrangement, taking the relative intensity of 

 the shadows produced, as a measure of the relative intensity of 

 light. The candle employed for the comparison was the patent 

 candle already referred to, and the burner was the kind known as 

 fish tail burner, which had been previously guaged, and known 

 to consume a trifle more than 5 cubic feet per hour with the 

 average maximum pressure of the gas works. I need hardly add 

 that the burner was the same in all the trials, and occupied 

 exactly the same position. The burner and the screen on which 

 the shadows fell were not moved at all during the experiments. 

 The only adjustment wanted was* to bring the candle nearer to or 

 father from the screen, and by beginning with the most luminous 



