AG SIXTH nEPoitT — 183C. 



On the Aqueous Sndi7ig-7'od Hydrogen Eudiometer. By R. Hare, M.D. 



In this instrument measurements are effected by the ingress or re- 

 gress of a graduated rod pressing air-tight through a collar of leather 

 into a copper tube, at the extremity of which a glass receiver is situated. 

 Tliis receiver terminates in an apex, with a capillary opening, which is 

 closed by a valve at the end of a lever actuated by a spring, when the 

 effect of the latter is not counteracted by the hand. The cavity of the 

 instrument being filled with water, and being perfectly air-tight, if the 

 rod be withdrawn to any sensible extent, while the orifice at the apex 

 of the receiver is closed, a vacuum ensues ; but if that orifice be open 

 the resulting vacuity becomes filled with the air, or with any other gas 

 by which it may be surrounded. 



To analyse the air, it is only necessary to take into the receiver, in 

 the first instance, one hundred measures of that fluid, and then intro- 

 ducing the apex into a bell glass containing hydrogen, to draw into the 

 receiver about fifty measures or more of this gas. By means of an arch 

 of platina wire within the receiver, so situated as to become the me- 

 dium of a galvanic discharge, the gaseous mixture being inflamed, and 

 all the oxygen, with twice its bulk of the hydrogen, consequently con- 

 densed, on introducing the instrument into water, so that the apex 

 may be just below the surface, the deficit produced by the combustion 

 is replaced by water ; and hence, on returning the rod carefully only 

 so far as to expel the residual gas, the number of graduations which 

 remain without the tube indicates the extent of the condensation. Of 

 this, one third is due to oxygen. 



Dr. Hare also exhibited some volumeters, or volume measures, by 

 which equal volumes of a gas may be taken with great accuracy. 



By means of one of these instruments a mixture of one part of hy- 

 drogen and two of air being introduced into a bell over the pneumatic 

 trough, on taking into the eudiometer 150 measures, and proceeding as 

 already described, the same results may be obtained, and perhaps with 

 more accuracy. 



As the pressure of the spring upon the valve, through the medium 

 of the lever, is not sufficient to resist the force of the explosion, the in- 

 strument is furnished with a kind of staple, moving on a hinge, and 

 furnished with a screw. By these means the valve is firmly held in its 

 place as long as is requisite, and afterwards easily released 1)y relaxing 

 the pressure of the screw and moving the staple on its hinge, so as to 

 get it out of the way of the lever, of which the extremity bearing the 

 valve is then easily raised by the pressure of the hand. 



ITie average results of some hundreds of experiments performed by 

 Dr. Hare with various instruments, as well as with that above described, 

 would lead to the conclusion that the quantity of oxygen in 100 mea- 

 sures of air is 20^^. 



Dr. Hare also presented to the Members of the Chemical Section 

 printed copies of a series of essays, not yet published, on different 

 subjects of chemical and electrical science, and descriptive of various 

 improvements in philosophical apparatus. 



