252 REPORT—1L840. 
seen. Very little of the zinc was dissolved, and a little loose 
oxides were in the bottom of the glass jar, which proved to be 
eta CO,)+ (CaO+CO,) +(FeO + Fe, O,) + (ZnO + Fe,O5) 
+ : 
225. A plate the same as the foregoing in all respects, im- 
mersed the same time in a saturated solution of common salt, 
on examination presented the same phenomena, but less strongly 
marked. 
Of the ratio of Zinked surface to that of Iron necessary to 
protect the latter, immersed in Sea Water. 
226. When equal parallelopipeds of partially zinked iron are 
immersed in sea water, having the following ratio of zinked 
surface to that of the iron, viz. 
Zinc Surface. Tron Surface. 
a ASO) (ecw ec) tis : oak shh togee 
B ZOOM Os PP : oes an 
Y TOO Ae - ri WH 8] | 
) On2 oie es 2 esr BEE: 
€ Ole. *. ung stom 
c 0:065 ste : se? eel! 
n OrOSTZ5: Ney : a Mek Mepil 
O 2B SM.. WOFOL5625 or > Seng 
Lae ey its ROOT OOrar as : odacher al 
the zinc is rapidly oxidized in all, and the amount of oxide of 
zinc formed is in the ratio of the surface of zinc exposed ; 
the other, or e—, elements being all of equal surface. The oxide 
of zinc formed is flocculent, and does not collect either at the 
iron or zinc poles, and is partly dissolved by the sea water. 
The iron remains bright and free from oxide, with every pro- 
portion of zinc, down to the ratio of 0°00786 :: 1 of iron. 
Hence the limit of protective power of zinc in metallic contact 
with iron immersed in sea water is between ;1,th and ;3,th 
of the surface of the latter, at which point oxidation takes place 
rapidly. 
Of Iron in metallic contact with Zine immersed in Fresh 
Water. 
227. When several equal parallelopipeds of iron are immersed. 
in fresh water, having the following ratios of zinked surface to. 
that of iron, viz. 
