220 WATER. 



The sliding rod eudiometer being ascertained to be tight, is filled 

 with water, free from air bubbles, the rod being introduced to its 

 hilt, and the valve at A being open, the rod is drawn out and the 

 instrument being in the atmosphere, common air of course en- 

 ters, or the eudiometer is placed under a bell glass, and the gas- 

 es, either successively, or previously mixed in the proper propor- 

 tions, are then introduced by suction of the graduated rod A, and 

 the wires W W being applied to the two poles of a calorimotor, 

 at the moment in action, the explosion takes place. The valve be- 

 ing opened under water, this fluid enters to supply the place of the 

 gases consumed, and any residuary air being excluded by the sliding 

 rod, the portion of the latter remaining without, will, by the gradua- 

 tion, indicate the deficit, which is to be apportioned by the rules given 

 below ; that is, f of the diminution is hydrogen, and is oxygen.* 



For the purpose of the general student, any mode in which the 

 mixed gases can be exploded conveniently and the diminution easily 

 ascertained, will answer every valuable purpose. 



USE OF THE HYDRO-OXYGEN EUDIOMETER. 



If we mix accurately 2 volumes of hydrogen with 1 of oxygen, 

 and inflame them in any of the above named eudiometers, provided 

 the gases are pure, there will be a total condensation. 



As it is however rare that the gases are quite pure, it is often best 

 to employ an excess of that gas which is used to detect the other. 

 In examining oxygen gas, if we take three volumes of hydrogen, 

 one third of the diminution being oxygen, it will not injure the result, 

 if there should be a residuum. If 100 measures of oxygen gas are 

 fired with 300 hydrogen, and there is a residuum of 130, it follows 

 that 270 have disappeared, and 90 is one third of this, and of course 

 it appears that there is 10 per cent, of foreign gas, it may be nitrogen, 

 or carbonic acid ; for there is an excess of 100 of hydrogen. 



Suppose, on the other hand, that we fire equal measures of oxy- 

 gen and hydrogen, say 100 of each; if the 200 are reduced to 80, 

 the diminution will have been 120, and two thirds of this, that is 80, 

 is owing to hydrogen ; it follows of course, that there is in the hy- 

 drogen 20 per cent of foreign gas most probably nitrogen. Henry. 



If 100 measures of common air are mingled with 50 of hydrogen, 

 and exploded, the 50 volumes will generally be reduced to 87, giv- 

 ing a diminution of 63 measures, one third of which, 21, is the pro- 

 portion of oxygen usually assigned to the atmosphere. 



* The figure of the calorimotor used in these experiments will he given under 

 the head of Galvanism. For a more detailed account, and various particulars to in- 

 sure accuracy, see Dr. Hare's Compendium. 



Not being in possession of the wood cuts of the barometer gage eudiometer, and 

 of the sliding rod gas measure, I have been obliged to omit an account of those in- 

 struments which 1 had prepared. 



