266 



BENJ. PIKES, JR., DESCRIPTIVE CATALOGUE. 



circular piece of wood, having on its surface a slip of ivory 

 inlaid, and furnished with a foot, which is fastened in the 

 middle of the bottom. 



To this* discharger belongs the small press (Fig. 287, pre- 

 vious page), the stem of which fits into the socket, instead of 

 the circular table. On the top of the stem are two oblong 

 boards, which are pressed together by means of two screws. 

 Between these boards may be placed any substance which re- 

 quires to be pressed while the electric fluid is sent through it. 



The construction of this instrument is such as to enable 

 the operator to use it with advantage in numerous experi- 

 ments, such as the oxidation of metallic leaves between slips 

 of card or of glass ; splitting small pieces of oak, firing 

 gunpowder, &c. 



By far the most interesting and brilliant application of the 

 powers of the Leyden jar is the melting of metallic wires. 

 When a strong charge is passed through a slender iron wire, 

 the wire is ignited or dispersed in red-hot globules. The 

 power of large batteries was formerly considered essential 

 to the production of this effect ; but if the wire be suffi- 

 ciently fine, a single jar, exposing a coated surface of about 

 190 square inches, Will be found sufficient to exemplify the 

 experiment. Price, $6.00 and 7.50. 



Fig. 288. Medical Jar. (Fig. 288.) This is like an or- 

 dinary Leyden jar, covered and lined to a certain 

 height with tin-foil, as at B. A wooden cap is 

 then prepared for it, and a hole just admitting a 

 glass tube, A, is bored in the middle of the cap. 

 The tube reaches below to within two inches of 

 the bottom, and projects upwards above the 

 cap, about three inches. This tube is also partly 

 lined and covered with tin-foil, so placed that 

 rather more than an inch of the glass is left un- 

 covered at the lower end, and about two inches 

 at the upper end. The tube is cemented to the 

 top of the bottle, and a smaller cap cemented on 

 the top of the glass tube ; but before this last is 

 cemented on, three holes are drilled in it ; one 

 for a hook wherewith to suspend the phial from the con- 

 ductor, the two others are to be left open ; one of them to 

 admit a wire to touch the inner coating of the tube, the 

 other a second wire, sufficiently long to reach to the coating 



