On the Corrosion of the Coppering of Ships. 207 
cess 1s repeated, and in a short interval afterwards the wood 
possesses the external appearance we have described. When 
the polish —— in brilliancy, it a be restored by the 
use of a little cold-drawn linseed oil.—Lond.- Jour. Arts, 
Vol. IV. p. 107. 
59. New Pyrophrous of Tartrate of Lead.-—In determining 
the composition of tartrate of lead, Dr. Friedmaun Gobel of 
Jena, observed that this salt when heated i in a glass vs form- 
ed a fine pyrophorus, ena portion of the deep brown 
mass is projected from the tube, it instantly tathde fire, and 
brilliant globules of metallic lead appear on the surface of the 
substance in ignition. The effect continues much longer 
than in other pyrophori.—Edinb. Phil. Journ. Vol. X. 
60. On the corrosion of the Coppering of Ships.—At a 
meeting of the Royal Society on the 22d January, Sir oad 
phrey Davy read a paper on the cause of the decay and corro- 
sion of the coppering of ships, which he ascribed to a constant, 
though feebie chemical action of the saline parts on the sur- 
face of the copper. ‘This action he. considers as galvanic ; 
and it is known, that some copper suffers comparatively 
little corrosion to that which takes place where the Coppa 
contains a small quantity of zinc or any other metal. In 
order to remedy this great pencciens evil, Sir Humphrey Davy 
has shown, that if a very small s arhane of tin is brought in 
contact with a surface of ieee one hundred times its size, it 
will render the copper so negatively electrical, that the sea- 
water is no longer able to corrode it. e same effect was 
produced when a small piece of tin was made to communi- 
cate with a large surface of copper by means of a wire. We 
opper. 
are informed by a friend (who saw the result of the experi- 
ment) that when a piece of Mr. Mushet’s patent copper, a 
piece of common copper, and a piece of the one rendered 
negatively electrical by zinc, were subjected to the action of 
salt water, the common copper was highly corroded, and the 
patent copper less so, while the negatively electrical co per 
was not affected at all. This elegant invention of Sir Hum- 
phrey Davy, will, we doubt not, be duly appreciated by the 
government and the p Abid. 
