136 On the Construction of De Luc's Columns. 



Art. XVII. — On the construction of De Luc's Columns, as modi- 

 fied by Zamboni: and on the modification of the single leaf Elec- 

 trometer contrived by the author, by which the possible efficiency of 

 a large electric series, may be ascertained, by testing a small por- 

 tion of the members of which it is to be constituted. Also on the 

 employment of the same instrument, as an Electrical Discrimina- 

 tor: by Robert Hare, M. D., Professor of Chemistry in the 

 University of Pennsylvania. 



Communicated by the Author. 



About fifteen years ago the construction of De Luc's electric col- 

 umns as modified by Zamboni, vi^as undertaken by Isaiah Lukens, one 

 of our most skillful and ingenious mechanicians. 



The materials employed were paper covered vrith leaf tin, (erro- 

 neously called silver paper,) peroxide of manganese, and crystallized 

 sulphate of zinc. . 



The peroxide was finely pulverized, and mixed with a concentra- 

 ted solution of the sulphate. The mixture thus formed was, by 

 means of a brush, applied like a pigment to the surfaces of the pa- 

 per not coated by the tin. The sheets were afterwards spread out 

 on the floor of an apartment and left during the night to dry. By 

 these means, unnecessary exposure to light was avoided, which Mr. 

 Lukens, conceives to be injurious, especially as received directly 

 from the sun. Next day the sheets were cut into disks of about five 

 eighths inch diameter, by means of a hollow punch. The disks 

 were then piled with the heterogenous surfaces alternating, as in 

 other voltaic series, and were introduced into, and compressed with- 

 in, glass tubes, accoutered as usual with pedestals, caps and bells. 

 Notwithstanding his skill and experience, Mr. Lukens, latterly com- 

 plained of occasional want of success, arising, ashe supposed, from 

 the defective quality of the manganese. In various instances, his 

 columns, after being completed with the utmost care, proved inert. 



The manipulation, likewise, according to his plan of operating, 

 appeared to me, lo be troublesome and precarious. He was accus- 

 tomed to place a row of 'the disks, as large as could be conveniently 

 handled, in a trough of sheet metal; and then transfer the pile thus 

 formed to the glass lubes. This operation, to be successful, requi- 

 red dexterity. 



