360 On the use of the Dynamic Multiplier. 



the filling up of the intervening space by deposit. A vast amount 

 of electricity is lost, by this necessary defect in common batteries. 

 The battery I have, has a lead cell, and can be depended upon at 

 all times, for a regular and powerful current. Any number of par- 

 allel plates may be mounted upon the same axis, and be used as a 

 simple or compound battery. 



When the battery is not in use, the zinc wheel is raised and sup- 

 ported between the upright pillars, by two cross bars. 

 Salem, Mass. April 19th, 1837. 



P. S. In my communication a few days since, I omitted to men- 

 tion the form of constant or protected battery, of which I sent you 

 a model. The truth is, it does not answer my expectations. When 

 first used, it was active and serviceable from its economy, but time 

 has proved it to be inferior to that of Mullen. As however I have 

 tried a great variety of forms, with a view of determining the best, 

 a few remarks may prove acceptable. 



On the use of protected batteries. — That which is known as Mul- 

 len's, where the copper cylinder is surrounded with membraae, con- 

 taining sulphate of copper, and the zinc plate outside, immersed in 

 some alkaline salt, appears to be the most active form of protected 

 batteries. But this battery is somewhat simplified, if the zinc plate 

 be protected in the same manner as the copper plate, and the cop- 

 per be made a tight cylinder, holding the sulphate. A considerable 

 saving is made, if the surface of the zinc plate not opposed to the 

 copper, be varnished or painted. The most active arrangement yet 

 tried, is made by using the nitrate of mercury as a substitute for the 

 salts of copper. The power of such a battery is so great, that the, 

 size may be very much diminished for common* experiments. Cyl- 

 inders of copper, two inches high, and an inch and a half in diameter, 

 are sufficiently large. The arrangement is the same as in Mullen's 

 battery, with a few exceptions ; the outer surface of the zinc cylinder 

 is varnished or painted, and likewise the inner surface of the copper 

 cylinder ; this last condition it is very necessary to observe. A little 

 battery of this description has been immersed without being replen- 

 ished seventy two hours, without any perceptible diminution of action. 

 The solutions used, are nitrate of mercury in the copper cylinder, 

 and nitrate of potash for the zinc. The great superiority of this bat- 

 tery over the sulphate of copper batteries, is due to the co-operation 

 of an independent chemical or electrical action, viz. the decomposi- 

 tion of the metallic salt by the copper plate itself. 



Salem, April 24th, 1837. 



