266 REPORT—1840. 
other materials, in order, by taking advantage of its positive re- 
lation to iron, to save the latter from the increased corrosion 
due to the presence of lead, which is strongly negative to it. 
Zinc alone, however, possesses some “disadvantages as a 
‘cramping ’’ metal; it oxidates with great rapidity when fused 
in an open vessel ; it contracts more than lead on solidifying, and 
it is too rigid to "permit subsequent “ caulking,”’ so as to cause 
it again to fill the cavity into which it was cast. ‘The results 
which have been given for the alloys of zinc with copper render 
it extremely probable, however, that an alloy of zinc and lead 
might be formed eminently suitable as a “ cramping metal” in 
contact with iron, which, while it should possess the requisite 
physical properties, would be found in such a relation to iron as 
to retard, or at least not promote, its oxidation. 
263. In my previous report* I suggested the possibility of 
preserving electro-chemically, to a greater or less extent, the 
dense and hard gray cast irons in ordinary use for engineering 
purposes by means of contact with the softest and most carbo- 
naceous cast irons, such as those of Scotland and Ireland. I 
showed that the latter sort of cast iron is, in presence of a sol- 
vent, constantly in an electro-positive relation to the former, 
and that of two such specimens of cast iron, in voltaic contact, 
there was reason to believe that the denser iron would be pre- 
served to a greater or less extent at the expense of the other. 
Experiments on this subject have now been in progress for 
twenty-five months. 
264. When four equal-sized parallelopipeds, two of very hard 
dense bright gray cast iron, just capable of being planed or 
turned, and two of soft dark gray and highly carbonaceous cast 
iron, are placed, one of each pair, separately in a jar of sea 
water, and the other pair (viz. hard and soft) in a jar of sea 
water together, and in voltaic contact, the pieces having been 
all weighed, and the sea water preserved at a constant level, 
&c. &c. Then, after a period of twenty-five months had elapsed, 
on examination the following were found to be the results as to 
corrosive action :— 
All the pieces were found covered with a coat of red oxide, 
having the composition = (Fe, O;) + (Fe O + C O,) +H O, 
and much of the same had deposited in the glass vessels. 
265. The piece of hard cast iron immersed singly was found, 
on washing off the coat of rust, clean and pretty bright, and its 
surface still metallic. On weighing, and also measuring by a 
micrometer, it was found to have lost a coat of iron over its 
* § 129. 
