ELECTRICITY. 485 



der or plate, will carry away from the leather a sufficient 

 quantity of amalgam, and will deposit it upon the rub- 

 ber. The leather with the amalgam needs not to be 

 kept in contact with the glass longer than while the cy- 

 linder makes eight or ten revolutions; moving, at the 

 same time the piece of leather with the amalgam from 

 one end of the cylinder to the other. Now if the cy- 

 linder be turned, and if the hand or the end of the fin- 

 gers be presented to it, a crackling noise, which is ac- 

 companied with numerous brushes in a dark room, indi- 

 cates that the cylinder is in good action ; and the prime 

 conductor being situated in its proper place, you may 

 proceed to perform the experiments. During the per- 

 formance, the electrified part of the machine is apt to 

 attract dust from all quarters, to obviate which the room 

 ought to be previously swept and dusted, and likewise 

 the operator ought to have a clean clolh at hand to wipe 

 off all particles of dust and filaments, which in spite of 

 all his precautions will frequently run to the cylinder, 

 to the conductor, &c. 



' The amalgam remains to he described. Mr Canton, 

 as far as we are informed, first applied the amalgam of 

 tin and mercury to the rubber of an electrical machine, 

 which was undoubtedly a capital improvement ; for by 

 this means an electrical machine will have its power 

 more than quadrupled. The tin amalgam is easily made, 

 for if you triturate tin foil and mercury, (in the propor- 

 tion of one of tin to two parts of mercury) in a mortar, 

 or even in the palm of your hand, the amalgam will be 

 formed in a minute or two. 



' The amalgam of mercury and any metallic substance 

 that may be amalgarned by it, contributes to increase 

 the electric power of glass, but some are more efficacious 

 than others. Mosaic gold has also been found efficacious 

 for the purpose of excitation. The zinc amalgam, how- 

 ever, which was first recommended by Dr Higgins, has 

 upon the whole been found the most efficacious. This 

 amalgam, which consists of one part of zinc with four or 

 five parts of mercury, is, according to Mr Cavallo, pre- 

 pared in the following manner. ' Let the quicksilver,' 

 he says, ' be heated to about the degree of boiling water, 

 VOL. i. NO. xx. 43 



