ON THE ACTION OF AIR AND WATER UPON IRON. 94] 
Coal-tar thus appears to stand preeminent as a covering varnish 
for iron. The general accordance of these experiments with 
those of the present report is satisfactory. The anomalous re- 
sult, No. IX., with the zinc protector, Mr. Prinsep considers due 
to its containing lead, which was proved to exist in it. Coal- 
tar was finally adopted for the iron vessels navigating the wa- 
ters of the Ganges. 
195. In the progress of these researches I procured, by the 
favour of Henry English, Esq., of the Mining Journal, a speci- 
men of “ zinc-paint’? now sold asa covering for iron when 
ground in oil; that which I received is in the form of a mode- 
rately dark, gray powder, which decomposes water rapidly ; suf- 
ficiently fine to form a strong full-bodied paint, when ground 
with oil, which dries rapidly, though not quite free from gritti- 
ness. As I could not obtain any very definite information as to 
the origin or mode of preparation of this substance, and its va- 
luable qualities were highly spoken of, I considered it worth 
making a quantitative analysis of. It will be unnecessary here 
to state the method pursued; the analysis was performed with 
care, and the results give the following composition as that of 
the zinc-paint : 
Sulphuret lead Sf ethene S905 
Sub-oxide and oxide of zine . . 4°15 
Mictallio Zine 2.5627 acess. ood 81°71 
Sesquioxide iron whe Rite ae 
Pale Mel ib. un Sh, Pali ig ADEE 
SEN Rl") be0s' sale 88 chs BO 
Bose. eek tie (iy hus. Wigiodeo4 
100 
It would hence appear to be probably some residual matter 
obtained in the zinc-works. Ihave at present specimens of it 
upon iron in all the six conditions of experiment, and hope at a 
future period to be able to report favourably of the results. I 
should, @ priori, conceive that it would make an excellent body 
for a sound durable paint, well suited to works in iron. 
196. Another sort of paint has been for some time much 
recommended by the vendors, made from impure black oxide 
manganese ground in oil. This may possibly form a powerful 
“drier,”’ but, from its harsh and dense substance, can never be 
a suitable “ body” for a paint; nor does it seem to offer any 
special advantage in the former respect. 
197. The defects of ordinary oil-paints seem chiefly to arise 
from the instability of constitution of the fat oils, turpentine 
or other organic substances entering into their composition. 
1840. R 
