160 



Dr. Andrew Fyfe on the Comparative Value of 



made with each coal, and the experiments with each gas were 

 frequently repeated ; and when it was necessary, other gases were 

 made, and the trials again repeated, so as to secure accuracy. 

 The consumption of the gas was ascertained in the usual way, 

 by an accurate experimental metre ; the trials with the specific 

 gravity, the pressure, and chlorine, being frequently repeated. 

 Instead of giving the names of the coals, I designate them by 

 letters. 



Gases. 



Illumina- 

 ting 

 power by 

 chlorine. 



Pressure 



at burner Square roots 



in J of 



lOOths of | pressures. 

 Inch. 



Durability by 

 metre, 1 foot 



min. 



Standard 



A. 

 Aa. 



B. 



Bb. 



C. 



Cc. 



D. 



Dd. 



E. 



Ee. 



F. 



G. 



H. 



I. 



K. 



24 



8 



11-5 



13 



15 



15 



15 

 17 



23 



24 



22 

 12 



22-75 

 12 



42 

 122 



80 



76 

 64 



72 



63 



60 

 56 

 40 

 38 

 50 



46 

 79 

 38 

 72 



6480 

 11045 

 8944 

 8717 

 8000 

 8485 

 7937 

 7745 

 74,^9 





6164 



7071 

 6782 

 8888 

 6164 



8485 





58 



50 



59-20 



63 40 



69-6 



65-50 



69 24 



72 



72 20 



88-53 



90-50 



77-30 



81-40 



62-30 



90-50 



65 



Durability 



calculated by 



square rool 



of 



pressure. 



/ It 



Difference be 



tween txpeii 



mental and 



calculated 



durability. 



49-49 



0-2 



61-36 



216 



63- 12 



28 



68-48 



0-17 



64-54 



56 



68-40 



1-4 



71 



10 



7115 



1-5 



87 



1-53 



90-48 



0-2 



77-48 



0-48 



81 



0-40 



61-58 



0-32 



89-18 



1-32 



64 • 54 



0-6 



Average of the errors between the experimental and the 

 calculated durability of the 16 trials, 



t " 



48 



From the foregoing table, it is evident, I think, that the mode 

 of finding the consumption by the pressure is sufficiently accurate 

 for all practical purposes. I mean, of course, merely with the 

 view of finding the durability of gases, as I do not propose it as 

 a method for superseding the use of metres, to ascertain the quan- 



tity of gas consumed by different individuals. I must mention 



3 



however, that in one or two instances, the observed pressure did 



not give the consumption, as indicated by the metre : whether 

 this was owing to a peculiarity in the gas, or to inaccuracy in 

 noting the results, I do not know. At the time that the exper- 

 iments were performed, the results were merely marked down, 

 and the calculations were made afterwards ; and after discovering 

 the want of correspondence, I had not then an opportunity of re- 

 peating the trials with the same coal, which was very remarkable 

 for affording a gas of very high illuminating power. This was 

 the more to be regretted, as the gas being at one extremity as to 

 quality, made it appear, that there was some deviation from the 

 rule I have laid down.* 



* Since writing the above, I have fortunately had an opportunity of procuring 

 the coal alluded to, and of preparing gas from it. All the trials were repeated with 



