234 NATIONAL ACADEMY OF SCIENCES 
a coating of zinc, of greater thickness on the surface containing the letters and 
figures. 
“From well-established principles of galvanism, and from the direct experi- 
ments of the committee, it is certain that while the zinc coating covers every part 
of the surface of the iron, no other galvanic action will take place than that 
exhibited in the ordinary corroding of a single metal, but that as soon as the 
smallest portion of the iron is exposed to the liquid precipitation from the atmos- 
phere, a galvanic current will be established passing through the liquid from the 
zinc to the iron, that the former will be more rapidly corroded than it was 
previous to the exposure of the iron, and that this action will go on until all the 
zinc is dissolved. The iron, during the process, will be protected from the action 
of the atmosphere at the expense of the zinc. After all the zinc has been dis- 
solved, the iron, being unprotected, will then be corroded in the usual manner. 
“ From this statement it is evident that the coating of zinc will tend to prolong 
the existence of the iron in its metallic state, though it will not afford a perpetual 
protection such as may be given by a coating of enamel like that used in covering 
the basins of iron sinks, kettles, etc. 
“The experiment made by the committee consisted in attaching to one end of 
the wire of a galvanometer a plate of zinc and to the other end a plate of iron. 
These two plunged in a vessel of water slightly acidulated by sulphuric acid, gave 
rise to a powerful current of galvanism from the zinc to the iron. While the 
zinc was rapidly corroded the iron remained unaffected. By substituting for the 
zinc a plate of copper, a still more powerful current was produced in the opposite 
direction. ‘The iron in this case was violently acted upon, while the copper 
retained its brightness. 
“The committee may state, as a general rule, that when two different metals 
are placed in metallic contact, the one most readily acted on by an acid will be 
dissolved, while the other will be protected, and that the action on the metal dis- 
solved will be increased in intensity by the association. “Thus, iron in association 
with zinc is protected, while the same metal in connection with copper is more 
rapidly corroded than it is without such connection. 
“ Respectfully submitted, 
“ Jos—EPH HENRY, 
“ J. He Cj CorEing 
“ JOSEPH SAXTON. 
“ GENERAL D. H. Rucker, U. S. A., 
“ Acting Quartermaster General.” 
It will be observed that this report refers exclusively to the 
metals composing the headstones and that the opinion expressed 
was that iron blocks would not endure perpetually. While the 
report was pending, a discussion of another character regarding 
