608 



GAS-METER 



the pipe D, and passes out again at the bottom of the tube c, into the meter ; the rest 

 of the gas enters the body of the meter through holes in the curved faces of the hoods 

 E E, and, after blowing on the glass cylinders, passes to the burners through the outlet 



To put the motor in action, lot the jet a bo lighted about an hour before the burners 

 are wanted. In most cases this jet will be lighted all day as a useful flame. Tho 

 hole a is so situated on the box c, that whatever be the size of the jet, a fixed tem- 

 perature is given to the box, that temperature depending on the quantity of flame in 

 contact with the box, and not at all on the length of the jet. Tho jet being lighted, 

 and the box c thereby heated, the gas which passes through it is raised to the same 

 temperature, and, flowing out at the tube c, impinges on the glass cylinder which 

 happens for the time to bo the lowest ; the heated gas soon raises a vapour in the 

 lower cylinder, the expansion of which drives the liquid into the upper one, until it 

 becomes heavier than the counterpoise /, when the cylinders swing on their centre, 

 the higher one descends, and comes in the lino of the current of hot gas, and the 

 lower one ascends ; the same motion continues as long as the jet a burns. The same 

 effect on the cylinder is maintained, however the outward temperature may change, by 

 the cold gas, which, issuing from the curved side of the hood E E, impinges on the 

 upper cylinder, and hastens the condensation of the vapoiir which it contains. 



The cold gas and the heater vary in temperature with the room, and thus counteract 

 each other. 



The lighting of the jet a is essential to the action of the meters ; in order to insure 

 this, the supply of gas to the burners is made to depend on it in the following manner. 

 The pipe o, by which the gas leaves the meter, is covered by a side valve, which is 

 opened and shut by the action of the pyrometer g ; the pyrometer is in communication 

 with and receives heat from the jet, and opens the valve when hot, closing it again 

 when cold. 



The speed at which the cylinders vibrate is an index of the quantity of heat com- 

 municated to them, and is in exact proportion to the quantity of gas blowing on them 

 through the pipe c and curved side of the hoods E E. 



The gas passed through the heater is a fixed proportion of the whole gas passing 

 the meter ; therefore the number of vibrations of the cylinder is in proportion to the 

 gas consumed. 



A trajn of wheel-work with dials, similar to that used in the common meter, 

 registers the vibrations. 



Simplicity, accuracy, and compactness are the most remarkable features of this 

 instrument, and the absence of all corrosive agents will ensure its durability. 



The most recently-constructed meters on the dry principle are those of Defines, and 

 of Messrs. Croll and Richards. Both of these contrivances consist in causing the 

 gas to fill expansible chambers of definite volume, and the alternate expansion and 

 contraction of these is registered by wheel-work. 



Defries' meter has three of these measuring chambers, separated from each other 

 by flexible leather partitions which are partly covered by metallic plates, to protect 



1068 



10C9 



them from the action of the gas. A A A A, fig. 1068, represent these metallic plates, 

 fixed upon the leather diaphragm nt n n. As the gas enters, it causes the flexible jar- 

 tition to expand, which it does by assuming the form of a cone, as seen in fig. 1069. 

 Three such chambers are attached to each meter, so as to insure a uniform and steady 



