226 ANNUAL OF SCIENTIFIC DISCOVERY. 



Pedro de Alcantaro was destroyed by an explosion off the coast of 

 Cumana, S. A., in the year 1815, and a large amount of coin sunk. 

 Within the past year, through the enterprise of our countrymen, a 

 portion of the silver dollars has been recovered. The coin was found 

 on a muddy bottom, a strong crust of coral having in some instances 

 formed over it. The pieces selected for the chemical trials exhibited 

 the average amount of corrosion, one the coinage of 1810, the other 

 1812. Dollars of these years in circulation weigh 412 grs. When 

 the corroded dollars had been carefully washed in water and acetic 

 acid, they were stripped of their coatings and weighed. That of 1810 

 weighed 330 grs., the loss being 82 grs., while the coin of 1812 simi- 

 larly treated lost 55.18 grs. The water and acetic acid had dissolved 

 a trace of chloride of copper and sulphate of lime ; the incrusting coat- 

 ing, which had been detached by means of a feeble galvanic current, 

 was a crystallized sulphuret of silver and copper ; even the small por- 

 tion of gold existing in that portion of the coin which was corroded 

 had also united to sulphur. Editors. 



CORROSION OF A COPPER ALLOY OF SILVER, USED AS SHEATHING 



FOR SHIPS. 



As a part of an extended investigation of the sea-water corrosion 

 of metals, carried on by Dr. A. A. Hayes, of Boston, it became an 

 interesting point to ascertain if an alloy of copper and silver would 

 rapidly corrode, under the ordinary exposures. Four complete suits 

 of sheathing copper, containing 4 Ibs. of pure silver in 2, 000 Ibs. of 

 alloy, were prepared by the Revere Copper Co. These were placed 

 as usual on vessels destined for long voyages, passing through dif- 

 ferent seas, and the results have been recently obtained. Quite unex- 

 pectedly, it has been found that the dense copper thus formed does not 

 resist sea-water corrosion so long as ordinary copper. But a fact more 

 surprising is, the corrosion of the alloy without the exercise of any 

 negative action on the part of the silver. It was assumed as a prob- 

 able condition, that, if the corrosion should be more or less rapid, the 

 silver would not be removed, but would be left with the partly cor- 

 roded surface. On the contrary, careful analyses of the corroded 

 sheathing and the assays of the masses resulting from the fusion of the 

 whole remaining copper alloy concur in exhibiting exactly the origi- 

 nal quantity of silver. 



INCRUSTATIONS IN THE BOILERS OF STEAM-ENGINES. 



A LETTER from Dr. .1. Davy to Dr. G. Wilson, on " the incrustation 

 which forms in the boilers of steam-engines," was read to the British 

 Association, at Edinburgh. The writer states that he has examined 

 specimens of such incrustations formed by deposition in voyages from 

 port to port in the British and Irish Channels and the North Sea, be- 

 tween Southampton and Gibraltar, in the Mediterranean and the Black 

 Sea, and in the Atlantic between Liverpool and North America and 

 between Southampton and the West Indies. " The character and 



