MAGNETISM AND ELECTRICITY. 159 
top, d, conical, with a rim above it perforated with numerous holes. The 
whole cylinder is inclosed in a bladder, g, fastened to the rim, e, above the 
holes ; a solution of sulphate of copper is poured upon the conical cover, d, 
which runs through the holes, f, and fills the space between the bladder and 
‘he cylinder, @ ; in addition, some lumps of sulphate of copper are laid upon 
the cover, being gradually dissolved by the fluid running over them. The 
bladder is inclosed in a hollow cylinder of zinc, h, with a longitudinal slit, 
which admits of a variation in its diameter. The whole is immersed in a 
glass or porcelain vessel, 1, containing weak sulphuric acid, or a solution of 
sulphate of zinc, common salt, or some other substance. The strong copper 
wires, p and n, soldered to the two cylinders, form the two poles of the battery. 
The constant battery of Daniel is not essentially different from that of 
Becquerel. This (pl. 20, figs. 59, 60) consists of a massive zinc cylinder, 
surrounded by weak sulphuric acid, placed in a bladder or a hollow cylinder 
closed beneath, of porous earthenware. The whole is set in a copper vessel 
filled with a solution of sulphate of copper. Fig. 59 exhibits the whole 
battery of ten elements; fig. 60, a section of the upper part of one element. 
abed is the principal copper vessel; efgh the porcelain or earthenware 
cylinder; m the zinc cylinder; ik a receiver attached to the upper part of 
the copper cylinder, perforated at the sides and bottom, and filled with 
pieces of sulphate of copper; these are constantly in contact with the fluid 
in the copper cylinder. Each zinc cylinder is connected with the copper 
cylinder of the succeeding element by a copper wire. 
Grove’s battery, consisting of zinc and platinum, is remarkably scsi 
one element is represented in pl. 20, fig. 61. The zinc plate is so bent as 
to form a cell, open above and at the two sides, in which stands a trough of 
porous porcelain, filled with nitric acid. A slip of platinum, nearly as broad 
and deep as the porcelain trough, is firmly clamped to the end, cd, of the 
zinc plate, dipping into the porcelain trough of the following pair. Each 
zinc cylinder thus inclosing a porcelain trough, is set in a glass vessel filled 
with dilute sulphuric acid, and the several elements, thus arranged, stand 
together on a wooden frame. Another, and perhaps more convenient 
arrangement, consists in having a zinc cylinder closed below, and with a 
binding screw attached. In this, when filled with dilute sulphuric acid, a 
porous cup containing nitric acid is placed. Over the whole there fits a 
wooden cover, from the middle of which hangs a slip of platinum foil or 
platinized silver, dipping into the acid. A second binding screw is in 
connexion with the upper end of the platinum. These two screws form the 
poles of the battery. 
The Carbon battery of Bunsen (pl. 20, fig. 62), not much less energetic 
than Grove’s, is yet much cheaper, the platinum being replaced by carbon. 
A cylinder of carbon, open at both ends, is placed in a glass vessel somewhat 
contracted above, and contains in its cavity a cylinder of porous clay 
closed below. There is a very slight interval between the two cylinders. 
The clay cylinder is filled with dilute sulphuric acid; the glass, however, 
contains concentrated nitric acid, which, after the immersion of the clay 
cylinder, fills the whole cavity up to the neck. The upper projecting 
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