3 68 ANNUAL OF SCIENTIFIC DISCOVERT. 



met'illic principles, electric currents may be thus formed wliich 

 will explain the magnetic action of the earth on the needle. 



M. Duchemin has succeeded in convincing the French govern- 

 ment that the destructive action of sea-water on metals may be 

 made to produce electrical currents for useful purposes, and ex- 

 periments are now being carried on to test the subject at the cost 

 of the Marine Department. Experiments tried during the summer 

 of 1866 gave promising results, and at the end of last September, 

 M. Duchemin was summoned to Cherbourg to assist the Commis- 

 sion in its labors. An experiment has been made before the 

 President of the Marine Council of Works, with 3 elements, each 

 about the size of a man's hat plunged in sea-water, at Paris, and 

 a sufficient electricity was produced to keep a Ruhmkorff coil of 

 16 inches in action, and produce sparks of two-lifths of an inch in 

 length. At Cherbourg, the currents of 7 elements plunged in the 

 sea, after having traversed more than 100 miles of copper wire, 

 made a needle deviate 8°. 



The Cherbourg Commission entered upon another kind of 

 experiment to ascertain whether these marine piles would not 

 protect iron from oxidation. When an iron pfete, of which the 

 surface had been cleaned, was placed in connection with the posi- 

 tive pole, it soon became completely oxidized, but it remained 

 unaffected when attached to the negative pole. Seven elements, 

 of 16 inches in circumference, sufficed to protect an iron plate, hav- 

 ing a superficies of several square yards, for an entire year, and at 

 the end of that period the elements themselves were in good 

 working order. The experiments made tend to show that the 

 zinc emploj'ed in his marine piles is capal^le of preserving from 

 oxidation a surface of iron equal to 18 times its own ; but, as the 

 chemical effect depends on the number of pairs, M. Duchemin 

 believes that a much hio;her result still is to be obtained, the 

 Commission having at present employed but a very small number 

 of elements. 



How, asks M. Duchemin, is the different action of the two poles 

 on iron to be explained? The ox3'gen obtained by electrical ac- 

 tion on water possesses energetic principles for oxidizing metals ; 

 the hydrogen produced in like manner possesses the contrary 

 power, which, however, is not evinced by hydrogen prepared in 

 the usual manner. A current of ordinary hydrogen passes through 

 a weak solution of perchlorure of iron containing a small quantity 

 of ferrocyanide of potassium without producing any effect, while 

 a current of hydrogen produced from sea-water produces a de- 

 posit of Prussian blue. 



A somewhat similar effect is observed, says M. Duchemin, in 

 the perchlorure of iron pile invented by himself and used at M. 

 Oudry's great galvano-plastic works at Passy. In this pile the ni- 

 tric acid is replaced by liquid perchlorure of iron and the acidu- 

 lated water by sea-water. The atlvantage of this over the Bunsen 

 pile is that it does not disengage h3-poazotic gases, which are 

 injurious to gold and silver deposits. 



Among the proposed applications of the marine pile is the pres- 

 ervation of the plates of ships lying in harbor, where, says M. 



