1871.] 



Constant Form of DanieWs Battery. 



255 



element thus arranged will undoubtedly continue remarkably constant for 

 many months ; but it has one defect, which prevents me from expecting 

 permanence for years. The zinc being below, must sooner or later, ac- 

 cording to the less or greater vertical dimensions of the cell, become 

 covered with precipitated copper from the sulphate of copper which finds 

 its way (however slowly) to the zinc. On the other hand, if the zinc be 

 above, the greater part of the deposited copper falls off incoherently from 

 the zinc through the liquid to the copper below, where it does no mischief, 

 provided always that the zinc be not amalgamated, — a most important con- 

 dition for permanent batteries, pointed out to me many years ago by Mr. 

 Varley. Placing the zinc above has also the great practical advantage that, 

 even when after a very long time it becomes so much coated with metallic 

 copper as to seriously injure the electrical effect, it may be removed, 

 cleaned, and replaced without otherwise disturbing the cell ; whereas if 

 the zinc be below, it cannot be cleaned without emptying the cell and 

 mixing the solutions, which will entail a renewal 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 degree 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 ad- 

 vantage in respect to permanence and ease of management, 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 gradu- 

 ally 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, 



