218 



WATER. 



bend is brought to the same level, and two inches or more of air is 

 left in the leg, which is held in the hand. The thumb is pressed 

 firmly upon the orifice, and the spark taken either through the hand 

 as a part of the conducting substance, or by a wire : the elastic spring 

 of the confined air prevents all danger of explosion, only a very slight 

 pressure being felt at the moment.* 



(c.) Volttfs eudiometer. I give, from 

 Dr. Hare, a figure of this elegant, but 

 expensive, and rather complicated in- 

 strument, which is now little used, and I 

 therefore omit the detailed description, 

 which may be found in Dr. Hare's Com- 

 pendium. 



A and G are graduated glass tubes : 

 each division of the 200 parts of A cor- 

 responding to 10 of G, which holds 10 

 measures of A. C is a funnel-shaped 

 foot, with a stop cock and cap for intro- 

 ducing gas from the measure, k, which 

 is furnished with a slide so as to give al- 

 ways the same measure. I is an insu- 

 lated electrical conductor. F, a basin 

 shaped cap for pouring in water, and to 

 admit of introducing G, air tight, with a 

 finger on the orifice, so that (F being 

 filled with water y ) it may be screwed to 

 its place, or removed from it without loss 

 of its contents. There is of course a 

 communication through B and E, and 

 the whole apparatus having been first 

 filled with water, the mixed gases are 

 introduced ; the spark taken ; B opened 

 under water to ascertain the diminution, 

 and the residual gas being let up into G 

 is there accurately measured. 



(d.) Dr. Hare's eudiometer. To 



produce the explosion of the gases, this 

 gentleman has availed himself of the ig- 

 nition produced by a small calorimeter, 

 in a slender platinum wire, forming a part of the connexion in the 

 interior of the eudiometer tubes : he measures the gas conveniently 

 and accurately, by a graduated rod, sliding air tight in the instrument, 



* For a more detailed description, see lire's Dictionary, art. Eudiometer; also 

 Edin. Phil, Trans. Jan. 1818, 



