Intelligence and Miscellaneous Articles. 391 



Two openings, exposed to the stream of the same volume of air 

 or gas, however they may differ in their respective areas, will always 

 admit quantities thereof strictly proportionate to those areas. Thus, 

 through a circular aperture of one inch in diameter, will pass precisely 

 sixty- four times as much air or gas as through a circular aperture of 

 only one-eighth of an inch in diameter ; and this will hold unerringly, 

 and under all pressures, allowing only for the additional friction the 

 gas is exposed to in passing through the "smaller opening, compared 

 to its friction through the larger one. This theory is so well authen- 

 ticated by practice, that it can require no further illustration here. 

 It is only the smaller quantity, therefore, or one-seventh part, of the 

 gas which it is necessary actually to pass through the working and 

 registering parts of the meter ; and from this portion being very 

 dry and at a high temperature, an immense advantage is derived ; for, 

 as the decomposing action on the materials of the meter ceases when 

 the gas is hot and dry, there will be little or none of that wear and 

 tear, going on so rapidly in the ordinary water meter, from the am- 

 monia, sulphur and galvanic action, which are the principal agents of 

 deterioration, and which also act (though not to the same extent) 

 upon other dry meters, only exposed to the usual aqueous vapour 

 which gas absorbs at the ordinary temperature of the atmosphere. 

 In hot dry gas the galvanic action ceases ; the ammonia, which exists 

 in the form of a gas, will, when not exposed to aqueous vapour, pass 

 off harmless ; but where there is moisture present, the ammoniacal 

 gas is instantly absorbed, and becomes a strong alkaline solution, 

 acting on the wrought iron parts of the meter. 



From Sir H. Davy's early experiments, it appears that (taking 

 weight) 100 grains of water absorbs thirty-four grains of ammoniacal 

 gas, consequently (taking bulk) one cubic inch of water takes up 475 

 cubic inches of that gas. [See Henry's Chemistry, vol. i. p. 397, 

 third edition.) The sulphur in the gas, combining with hydrogen, 

 forms sulphuretted hydrogen gas. Water absorbs twice its own bulk 

 of this gas (see the same Avork] , and when so impregnated, the gas 

 is very destructive to brass and copper ; but, when dry, it is harmless. 



It will be observed that, in the dry meter now describing, all those 

 parts which are exposed to six -sevenths of the whole quantity of 

 gas admitted, consist either of cast iron, pure tin, or German silver, 

 none of which materials are acted on injuriously by gas in the usual 

 state of the atmosphere ; and as there is no water, and the remaining 

 (only one-seventh) part of the gas working through the meter at a 

 high temperature, the action of decomposition on the materials is 

 altogether avoided. 



All these requisites having been most conclusively determined <X 

 priori, it may be proceeded to consider the arrangements necessary 

 to put the above philosophical facts to practical application in the 

 construction of the " New Differential Dry Gas-light Meter." 



First, the two glass cylinders, as previously described, are to be 

 suspended in such a manner that the alcohol may be expelled from 

 the one cylinder placed in the lowest position, and driven to occupy 

 the other cylinder placed in a higher position ; this being effected, 

 the upper cylinder will descend and act as a pendulum, imparting 



