On the Corrosion oj the Coppering of Ships. 207 



cess is repeated, and in a short interval afterwards the wood 

 possesses the external appearance we have described. When 

 the polish diminishes in brilliancy, it may be restored by the 

 use of a little cold-drawn linseed oil. — Lond. Jour. Arts, 

 Vol. IV. p. 107. 



59. JV*ew Pyrophrous of Tartrate of Lead. — -In determining 

 the composition of tartrate of lead. Dr. Friedmaun Gobel of 

 Jena, observed that this salt when heated in a glass tube, form- 

 ed a fine pyrophorus. When a portion of (he deep brown 

 mass is projected from the tube, it instantly takes 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 Hum- 

 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 feeble chemical action of the saline parts on the sur- 

 face of the copper. This action he considers as galvanic j 

 and it is known, that some copper suffers comparatively 

 little corrosion to that which takes place where the copper 

 contains a small quantity of zinc or any other metal. In 

 order to remedy this great practical evil, Sir Humphrey Davy 

 has shown, that if a very small surface of tin is brought in 

 contact with a surface of copper one hundred times its size, it 

 will render the copper so negatively electrical, that the sea- 

 water is no longer able to corrode it. The 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 

 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 copper 

 was not affected at all. This elegant invention oi Sir Hum- 

 phrey Davy, will, we doubt not, be duly appreciated by the 

 government and the public. — Ibid. 



