FRANKLIN'S PLATE. 619 



is so great, in consequence of the layer of fat, that they cannot be 

 separated otherwise. 



The vessel in which the sealing-wax has been melted may be 

 cleaned by boiling in it a little of a strong aqueous solution of soda, 

 which dissolves the sealing-wax. 



The plate of sealing-wax is exceedingly brittle, and must therefore 

 be handled with great care ; it should not be preserved by keeping 

 it between the discs, but upon some support, with a sufficiently 

 large, flat surface, as otherwise it would become bent in the summer. 

 The support should be slightly greased to prevent the plate from 

 adhering. 



Before using the plate the adhering fat or oil should, for the sake 

 of cleanliness, be carefully wiped off, although its presence would by 

 no means interfere with the experiments, since oil and fat are good 

 insulators. 



If a condenser is only to be used for accumulating large 

 quantities of electricities, the two conductors may be 

 firmly connected with the insulator, since the necessity 

 for separating the essential parts from each other arises 

 only when the mode of action is to be investigated by 

 means of the electroscope. 



A very simple form of the condenser, called ' Frank- 

 lin's plate/ resembles very much the apparatus just 

 described. It consists of a rectangular or sometimes 

 round plate of glass, on each side of which pieces of tin- 

 foil are fastened opposite to each other, leaving a space 

 of a few centimetres free all round the edge. 



A Franklin's plate or pane may be easily constructed by having a 

 plate of well insulating glass cut by a glazier so as to fit into the 

 wooden frame of a common slate, as used by school children, the 

 slate being taken out. Pieces of tinfoil are pasted upon both sides ; 

 they should everywhere be about 2 cm from the wooden frame. It is 

 well to cover the intermediate portions with an insulating layer of 

 shellac varnish. Into the middle of one edge of the frame a short 

 piece of stout wire is driven, leaving a portion to project, which is 

 bent into a ring for attaching a chain by which communication may be 

 established with the ground. The ring is connected with one of thp 



