Mr. W. De la Rue on Voltaic Electricity. 485 



and a piece of zinc, coiling the two to form a small calorimotor, 

 which is to be put into a glass jar filled with a solution of sulphate 

 of copper, and inverted in a vessel of the same ; metallic copper 

 and its oxide will precipitate, and hydrogen gas fill the jar. 



Seeing the effects so continuous in a simple battery, I tried 

 a Cruickshank's, of one hundred pairs, each plate exposing to 

 the action of the fluid a surface of twenty-five square inches. 

 This was charged with a saturated cold solution of sulphate of 

 copper, to each three gallons of which I added two ounce mea- 

 sures of nitric acid, for the purpose of cleaning the plates and 

 freeing them from oxide; for half an hour the action was so 

 feeble that I was on the point of emptying the trouo-h, but I 

 soon after noticed that the effect was rapidly increasitig ; I was 

 then induced to proceed. The batteries attained their maxi- 

 mum of power in three quarters of an hour after charo-ino-. 



Charcoal points were vividly and continuously ionited^ the 

 arc passing through a space of three eighths of an inch; this 

 experiment was beautifully varied by dipping the charcoal in 

 nitrate of strontian, the arc then being of a crimson colour. 



Steel points of wire, a quarter of an inch thick, were then 

 tried; the arc passed through an equal space; the steel ra- 

 pidly fusetl, was deflagrated, and by the scintillations pro- 

 duced a beautiful effect. 



Copper points treated in a like manner produced a green 

 arc, and were rapidly destroyed. 



Brass produced a blueish white arc; and the more fusible 

 metals, such as bismuth and tin, produced likewise an arc, but 

 the metal was soon carried from one point to the other and 

 established a perfect contact. 



A piece of platina wire, one eighth of an inch thick, was ra- 

 pidly fused, by keeping it at a short distance from a disc of 

 copper, so as to allow the arc to pass from it to the disc. 



A heap of metallic leaves was burned with rapidity. 



Thick tin-foil was deflagrated. 



Very thick zinc-foil was rapidly consumed. A bunch of 

 needles burned rapidly in mercury ; the end of a file was defla- 

 grated in the same manner. 



Extraordinary as was the power of deflagrating metals, tiie 

 effect of igniting was comparatively small ; not more than an 

 inch of iron wire could be ignited, though, if only twelve pairs 

 of Wolluston's four-inch plates were used, charged with tlie 

 sau)e solution, two and a half inches could be kept ignited for 

 some time. 



The battery was then tried in decomposing common caustic 

 potash, which it did with facility; the combustion of the po- 

 tassium evolved, vividly igniting the thick platinum wire used 

 for the negative pole. These experiments occupied about two 



