| Hare’s Eudiometers, &c. ae 
round or bottle. The acid solution must occupy the lower 
half of the vessel, unless when the plunger raises it. 
I am under the impression that there is no 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. Atmf, 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. Aton, is the neck of the recipient, 
ground to fit the recurved tube which enters it. AtS, is 
a screw, by which to close the capillary orifice of the recip- 
ient. 
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. 
Fig. 3. Displays a construction of the sliding rod, by 
which, when desirable, greater accuracy may be attained in 
the 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 into 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- 
drogen gas. Moisture in the air suspends the action of that 
apparatus, but does not interfere with the one here repre- 
sented. 
Vous LU. ..No: 2: 41 
