Intelligence and Miscellatieous Articles. 335 



which enable the points of junction to be removed to a distance from 

 the furnace. 



Third experiment. — By the substitution of a cylinder of charcoal 

 prepared in the usual manner for the iron rod, connecting it by 

 means of a platinum wire with the tangent magnetoscope, a current 

 passing in the same direction as that furnished by the iron and 

 copper, was produced. In this case then we have the current 

 resulting from the combustion of the charcoal. 



By comparing in the same manner as with the iron, the current 

 l)roduced by charcoal and copper with that of a nitric acid couple, 

 the following results are obtained, — 



a;-fy=sin 14°-30=25038 

 ^~y=sin 8°-50=: 15357, 

 hence a?=20197, y=5340, and consequently x \ y w 3*76 : 1. 



Fourth experiment. — To compare these two sources of electricity 

 exactly, it is necessary to determine, by means of Ohm's law, the 

 conductive power of the sources themselves. The experiments 

 which I have hitherto made show, that under the most favourable 

 circumstances, when the temperature approaches the melting-point 

 of copper, the conductive i)Ower of the two sources is nearly the same, 

 but in proportion to the distance from this point the resistance 

 gradually increases in the pyro-electric couple. 



Fifth experiment. — The pyro-electric currents produce chemical 

 decompositions like other currents. 



With two plates of platinum and a Bunsen's couple, water is 

 decomposed pretty rapidly, whilst with a pyro-electric couple acting 

 at a temperature far below the melting-point of copper the current 

 is distinctly stopped, at least if the positive platinum plate be not 

 replaced by a plate of copper ; in this case the disengagement of 

 hydrogen gas is tolerably abundant. The same thing takes place 

 when a solution of sulphate of copper is substituted for the acidulated- 

 water ; with two plates of copper the sulphate is decomposed. 



Observations. — The pyro-electric couples may be prepared in va- 

 rious ways, I shall mention three : — 



1. Into an ordinary reverberatory furnace, an earthen crucible 

 is introduced, lined internally with a thick plate of copper, turned 

 so as to fit the interior of the crucible, and furnished with a wire of 

 the same metal passing through an earthen tube to preserve it from 

 oxidation. The crucible is filled with pounded glass, in sufficient 

 quantity to cover the plate of copper, when fused, to a thickness of 

 two centimeters. In contact with the glass, and resting vertically 

 upon one end, is placed a bar of iron, long enough to pass through 

 the top of the furnace ; to the upper end is attached a wire of the 

 same metal, which serves both to maintain it in its proper position and 

 to connect it with the tangent magnetoscope or any other apparatus. 



2. After filling the crucible 'with pounded glass to which 0*25 of 

 carbonate of soda has been added to hasten the fusion, two long 

 rods of iron and copper are introduced into it, and maintained in a 

 vertical position, without contact, by means of iron and copper wires 

 attached to their free extremities, which also serve as conductors. 

 As soon as the glass is fused, the oxide of iron formed is dissolved. 



