the preservation of metals by electro-chemical means, 333 
tain by means of this balance, a diminution of weight upon so 
large a quantity, equal to 1 05 of a grain. It was evident from 
a very minute inspection of the sheet with the largest quan- 
tity of protecting metal, that there was not any adhesion of 
alkaline or earthy substances to its surface. 
Having observed in examining the results of some of the 
experiments on the effects of single masses of protecting 
metal on the sheeting of ships, that there was in some cases 
in which sheets with old fastening had been used, tarnish or 
corrosion, which seemed to increase with the distance from 
the protecting metal, it became necessary to investigate this 
circumstance, and to ascertain the extent of the diminution of 
electrical action in instances of imperfect or irregular con- 
ducting surfaces. 
With single sheets or wires of copper, and in small confined 
quantities of sea water, there seemed to be no indications of 
diminution of conducting power, or of the preservative effects 
of zinc or iron, however divided or diffused the surface of the 
copper, provided there was a perfect metallic connection 
through the mass. Thus, a small piece of copper containing 
about 32 square inches, was perfectly protected by a quantity 
of zinc which was less than part of the whole surface ; 
and a copper wire of several feet in length was prevented from 
tarnishing by a piece of zinc wire which was less than 
part of its length. In these cases the protecting metal cor- 
roded with great rapidity, and in a few hours was entirely 
destroyed ; but when applied in the form of wire and covered, 
except at its transverse surface, with cement, its protecting 
influence upon the same minute scale was exhibited for many 
days. A part of these results depend upon the absorption 
