Mvthod of fitting up Mr\ Be Luc's Electric Column. 205 



Ekeberg to be 7*953 ; and I have every reason 4o suppose 

 their results correct, since a Bniall fragment of the former 

 appeared upon trial to be 5*87, while a specimen of tanta- 

 lite, weighed at the same time, was as much as 7*8. I 

 should, however, observe, that the specific gravities of 

 three other fragments borrowed for this purpose were not 

 so high, that of one being 7*65, of another 7*53, and of a 

 third so low as 7*15. 



It is evident that no variation of mere proportion of the 

 ingredients can account for an increase of specific gravity 

 from 5*918 to 7*953, vvhich are in the ratio of 3 to 4 ; foV 

 since columbite contains four fifths oxide, if the whole re- 

 maining one fifth part in weight of that oxide could be 

 supposed added to the same bulk, without diminution of 

 the quantities of iron and manganese, the specific gravity 

 would not then exceed 7*1 ; and even if a weight equal to 

 one third of the whole were thus added, without increase 

 of, bulk, still the aggregate would not quite equal the 

 heaviest tantalite in specific gravity; but, on the contrary, 

 fhe quantity of white oxide in this specimen certainly does 

 not amount to six sevenths, and probably is not more than 

 five sixths of the whole mass. 



The only chemical difference, by vvhich this circumstance 

 could be explained, would be the state of oxidation, which 

 my experiments cannot appreciate ; but it may also arise 

 in part from actual cavities in the mass of columbite, and* 

 in part from the state or mode of aggregation. 



XXXV. Desciiption of a Method of jetting up in a portable 

 Form The Electric Column lately invented by J. A. De 

 Luc, Esq, Jlso an Account of several Experiments^ 

 made ivith it. By B. M. Forster, Esq, 



To Mr, Tilloch, 



Sir, Jliaving been informed that a rovv of galvanic plate? 

 had been constructed without any fluid being interposed, and 

 that it acted very sensibly on a gold-leaf electrometer, I 

 formed one, of about two hundred small circles of zinc, and 

 the same number of blotting-paper and Dutch gold-leaf, the 

 Putch leaf being cemented on the paper with a solution of 

 gum arabic ; the blotting-paper was double, two pieces 

 were gummed or pasted together before the Dutch leaf was 

 put on. Through these circles, or plates, a silken string w as 

 passed for connecting them together. This small instru- 



meut 



