tfilli a large Voltaic Battery. 415 



bably be deemed fatal to the opinion of those mineralogists (if 

 any do still maintain that ojiinion) who class the diamond with 

 substances of the siliceous genus. 



When dry caustic potash was exposed to the intense heat be- 

 tween the two pieces of charcoal, it fused, and appeared to de- 

 compose, throvviug off a large flame of the peculiar purple-retl 

 colour that attends the combu'^tion of potassium. \Vheu moist 

 caustic potash was placed in the circuity the water only was de- 

 composed. 



I endeavoured to ascertain if there be any difference in the 

 degree of heat produced at either pole of the battery, bv placing 

 two small earthen-ware cups, each containing an equal weight 

 of mercury, in the circuit, and connected together by a platina 

 wire of such size and length as to be kept constantly ignited. 

 The mercury in the cup connected with the zinc end of the bat- 

 tery, attained in 20 minutes the temperatiue of 121°; thr.t in 

 the other cup 112'. 



The battery, even in its most active state, communicated n» 

 charge to the Leyden pl>i^al. 



I give the following ex'j)eriinent, the last with which I shall 

 occupy the time of the Society, without comment. I separated 

 all the zinc from the copper plates, by dividing the leaden straps 

 that united them ; and then by means of other leaden straps, i 

 connected all the zinc plates together as one plate, and all the 

 copper plates in the same manner ; thus reducing the whole bai- 

 tery to only two plates, each prer^nting a surface of 1344 square 

 feet, reckoiiing the coj'per sur; sve as only equal to the zinc. 

 When the plates, thus arrangeci, were suspended, quite out of 

 contact with the acid, a communicauon was made between the 

 two metallic surfaces by viY::.\.'i of a platina wire -j^Vo^-c-udth of aa 

 inch diameter, and about -^i\'i of an inch ioi g, with every possi- 

 ble atter.tion to ensure a perfect contact ; h>ut, although the ex- 

 periment was made in the dnrk, not the slightest appearance of 

 ignition was perceptible in the minute wire by which these ex- 

 tensive surfaces were connected. It is known, I believe, to al- 

 most every member of this Society, that Dr. Wollaston ha? 

 shown, with the delicate apparatus invented by him, that a pla- 

 tina wire, of the same dimensions as that just mentioned, is in- 

 stantly ignited by a single pair of plates one inch square, on 

 beir;;j; immersed in a diluted acid. The ratio of the areas of the 

 plates of llie respective batteries is as 1 to 48384. When the 

 plates of the large i)atterY, in the usual order of arrangement, 

 were inmiersed in mere pump water, previous to any acid having 

 been put into the cells, they ignited jth of an inch of platina 

 wire -i--nTrth of an inch diameter, and fused the end of it into .i 

 perfect globule, 



LXXV. On 



