Hare’s Eudiometers, &c. 317 
round or bottle. The acid solution must occupy the lower 
f of the vessel, unless when the plunger raises it. 
T am under the impression that there isno form in which 
a pair of galvanic surfaces can be made so powerful in pro- 
portion to their extent, as in that above mentioned. ‘The 
zinc-is every where opposed by two copper surfaces by 
having this metal only a small fraction in excess. 
; Explanation of the Plate. . 
(See the end of the volume.) 
Fig. 1. Sliding rod eudiometer or gas measure, sur- 
mounted by its spheroidal recipient. rr, sliding rod gradu- 
ated into twenty divisions, each subdivided into ten, so as 
to make two hundred parts. Atm f, are male and female 
screws, (forming: what mechanics call a stuffing box,) by 
means of which a cork soaked in beeswax and oil is com- 
pressed about the rod. Atn, is the neck of the recipien 
ground to fit the recurved tube which enters it. At » is 
a screw, by which to close the capillary orifice of the recip- 
tent 
_ Fig. 2. Eudiometer upon the same principle, but made 
stouter, in order to resist the explosion of inflammable mix- 
tures. W W, wire to be ignited. es 
__ Fig. 3. Displays a construction of the sliding rod, b 
which, when desirable, greater accuracy may be attained in 
€ measurement of gas. A smaller rod or wire is made to 
slide within the larger. Whatever may be the ratio (in 
_ bulk) of the rods to each other, the lesser may be graduated 
to give thousanths, by ascertaining how far it must be mov- 
ed to produce the effect of a movement of one division on 
the larger rod, and dividing the observed distance mto ten 
parts, | 
_ Fig. 4. Represents an apparatus adapted to explode an 
inflammable mixture, as mentioned in the preceding article, 
and so contrived to be a substitute for the well known ap- 
paratus in which an electrophorus is employed to ignite hy- 
rogen gas. Moisture in the air suspends the action of that 
apparatus, but does not interfere with the one here repre~ 
_ Sented. 
Vou. IL.....No. 2 Ai 
