﻿540 Royal Society : — 



the cell ; whereas if the zinc be below, it cannot be cleaned without 

 emptying the cell and mixing the solutions, which will entail a re- 

 newal of fresh separate solutions in setting up the cell again. I have 

 therefore planned the following form of element, which cannot but 

 last until the zinc is eaten away so much as to fall to pieces, and 

 which must, I think, as long as it lasts, have a very satisfactory de- 

 gree of constancy. 



The cell is of glass, in order that the condition of the solutions 

 and metals which it contains may be easily seen at any time. It 

 is simply a cylindrical or rectangular jar with a flat bottom. It 

 need not be more than 10 centimetres deep ; but it may be much 

 deeper, with advantage in respect to permanence and ease of ma- 

 nagement, when very small internal resistance is not desired. A disk 

 of thin sheet copper is laid at its bottom. A properly shaped mass 

 of zinc is supported in the upper part of the jar. A glass tube (which 

 for brevity will be called the charging-tube) of a centimetre or more 

 internal diameter, ending in a wide saucer or funnel above, passes 

 through the centre of the zinc, and is supported so as to rest with its 

 lower open end about a centimetre above the copper. A glass siphon 

 with cotton-wick core is placed so as to draw liquid gradually from 

 a level about a centimetre and a half above the copper. The jar is then 

 filled with semisaturated sulphate-of-zinc solution. A copper wire 

 or stout ribbon of copper coated with india-rubber or gutta percha 

 passes vertically down through the liquid to the copper plate below, 

 to which it is riveted or soldered to secure metallic communication. 

 Another suitable electrode is kept in metallic communication with 

 the zinc above. To put the cell in action, fragments of sulphate 

 of copper, small enough to fall down through the charging-tube, 

 are placed in the funnel above. In the course of a very short time 

 the whole liquid below the lower end of the charging-tube becomes 

 saturated with sulphate of copper, and the cell is ready for use. It 

 may be kept always ready by occasionally (once a week for instance) 

 pouring in enough of fresh water, or of water quarter saturated with 

 sulphate of zinc at the top of the cell, to replace the liquid drawn 

 off by the siphon from near the bottom. A cover may be advan- 

 tageously added above, to prevent evaporation. When the cell is 

 much used, so that zinc enough is dissolved, the liquid added above 

 may be pure water ; or if large internal resistance is not objected to, 

 the liquid added may be pure water, whether the cell has been much 

 used or not ; but after any interval, during which the battery has 

 not been much in use, the liquid added ought to be quarter-sa- 

 turated, or even stronger, solution of sulphate of zinc when it is 

 desired to keep down the internal resistance. It is probable that one 

 or more specific-gravity beads kept constantly floating between top 

 and bottom of the heterogeneous fluid will be found a useful adjunct, 

 to guide in judging whether to fill up with pure water or with sul- 

 phate-of-zinc solution. They may be kept in a place convenient for 

 observation by caging them in a vertical glass tube perforated suffi- 

 ciently to secure equal density in the horizontal layers of liquid, to 

 be tested by the floaters. 



