Intelligence and Miscellaneous Articles. 393 



sary to dwell particularly on this part of the arrangement, which is 

 absolutely essential to the correct registration of the meter, and which 

 has been contrived in so complete and effective a manner, and by 

 means which cannot possibly be deranged. 



The preceding are the leading features of this philosophical ar- 

 rangement for measuring the flow of gas of a given quality. With 

 the same heat the same results will obtain ; the only variation that can 

 take place must be by change of temperature of the small jet of 

 flame which issues from the hemispherical end of the solid brass 

 cylinder, this being the governing principle ; consequently, with an 

 increased temperature of the solid brass knob, caused by a brighter 

 name (and which imparts its heat to the tube or receptacle for the 

 gas, called the heater), or vice versd (the same quantity of heated gas 

 being discharged on the lower glass cylinder), the flow of alcohol 

 from the one cylinder to the other, and consequently the vibrations 

 will be quicker or slower in exact proportion to the difference of 

 temperature. Hereby is obtained a measure of light ; in fact, a photo- 

 meter, that is, a light-meter; in other words, a gas-light meter, 

 rather than gas-meter, which is the more accurate definition, since 

 the article to be measured is light, not gas ; for it is well known that 

 the illuminating power of coal gas varies 30 per cent., according to the 

 process used in its production, and the quality of the coal from which 

 the gas is obtained. 



The principle of this meter being based on the fact, that the in- 

 tensity of the heat from a gas flame is as the brightness or illumi- 

 nating power, it may be well, for the information of those who have 

 not made this branch of chemistry their study, to give the following 

 short extracts from the most approved authorities : — 



From Dr. Henry's Experiments on Coal Gas, published in the 

 Manchester Philosophical Transactions : — 



" By the first train of experiments, I endeavoured to derive, from 

 a careful analysis of the compound combustible gases, a measure of 

 their illuminating power, admitting of more exact appreciation than 

 the optical method of a comparison of shadows. The one which I 

 was led to propose as the most accurate, and, I still think, entitled 

 to preference, was the determination of the quantities of oxygen 

 gas consumed, and of carbonic acid formed by the combustion of 

 equal measures of the different inflammable gases, that gas having 

 the greatest illuminating power which in a given volume consumes 

 the largest quantity of oxygen. The average results of a great 

 variety of experiments were comprised in the following table : — 



Oxygen gas required Carbonic acid 



Kinds of gas. to saturate 100 measures. produced. 



Pure hydrogen 50 — 



Gas from moist charcoal . . 60 35 



Ditto from wood (oak) ... 54 33 



Ditto from dried peat ... 68 43 



Ditto from cannel coal . . . 170 100 



Ditto from lamp oil .... 190 124 



Ditto from wax 220 137 



defiant 284 179." 



