Different Kinds of Coal for the purpose of Illumination. 161 



From the foregoing experiments, ;t is evident that the durabil- 

 ity of a gas can be easily ascertained, by using a burner with an 

 aperture of a certain diameter, having a scale for measuring the 

 height of flame, and a gauge for observing the pressure, at which 

 : the gas is burning, at that height of flame j of course taking care 



to make the measurement with accuracy. The consumption of 

 any gas by this burner, with the height of flame fixed on, is first 

 to be determined by metre, numerous trials being made ; while, 

 at the same time, at each trial, the pressure is also noted. By this 

 means, and taking the average of all the consumptions and pres- 

 sures, a standard is obtained. Suppose that with a flame of 5 

 inches, and a pressure of //?&* at the burner, the consumption of 

 a gas is, by metre, found to be one foot in 65 minutes ; and that 

 another gas requires, with the same burner and height of flame, 

 a pressure of T V\iths; the square roots of these pressures are 

 8560254 and 9695359 ; then, as the latter is to the former so is 

 65, the time for the consumption of the latter, to 5721. which is 

 the time for the consumption of the former. Now 8560254 x 

 65 = 5564165; accordingly, this number divided by the square 

 roots of the pressures necessary for the consumption of other 

 gases, will give the times for the consumption of these gases, 

 when consumed with the same burner, and with the same height 

 of flame. 



The jets now in general use, vary from the 2Sth of an inch, 

 as recommended by Christ ison and Turner, to the 45th of an 

 inch. Most of the trials which I have now recorded, were made 

 With a jet of the 33d of an inch ; not because I prefer it, but be- 

 cause I had begun my investigations with it, without being aware 

 °f the practical applications to which the results might lead ; 

 and having once begun with it, I thought it better to complete 

 the experiments with it. 



Since these experiments were finished, I have performed others, 

 to enable me to find the best jet for the purpose now recom- 

 mended. I had accordingly jets made with accuracy, the aper- 

 tures in which were the 25th, 30th, 35th, 40th, 45th, and 50th 

 °f an inch ; with all of which numerous trials were performed, 

 to ascertain the consumption and pressure. I soon, however, reject- 

 ed the first two, because they gave an unsteady flame : while the 

 Pressure-column in the gauge was not of any great length. With 

 the remainder, the flame was more steady, and more easily meas- 

 ured, while the pressure column was of sufficient length to be 

 e asily marked. I soon, however, also, rejected the burner. No. 

 5 0, because unless the pressure on the street-pipes is great, it does 





great care, and were found to give results corresponding with those in the above 

 table, so that there must have been an error in noting the results of the first trials. 

 In the subsequent trials, repeated again and again, the consumption by metre and 

 calculated by pressure differed only in 40 seconds. 

 Second Series, Vol. VII, No. 20.— March, 1849. 21 



