201 



down three or four times a day, with two labourers, who remain 

 down about two hours at a time. During the past season they have 

 brouo-ht up a quantity of copper, in various shapes, besides cannon- 

 balls, &c. ; and Spanish dollars, the recoinage of which at the Mint 

 has produced about $18,500. The silver has been much corroded by 

 the action of sulphur, which is supposed to have occurred from the 

 usual precaution of placing the specie in the powder magazine. This 

 has occasioned a diminution in value of 7 or 8 per cent., that is, the 

 dollars average 92 or 93 cents each ; but the variation of loss is 

 very great, as some are found worth 98 cents, and one, with the 

 stamps still visible, was reduced to 34 cents in value. They are all 

 too much spoiled for currency, though in most cases the impressions 

 are very distinct. 



The cannon-balls and grape-shot are highly oxidized, and are curi- 

 ous from having lost so much in weight; the shot herewith shown, 

 being 2 inches in diameter, must have originally weighed just 18 ozs. 

 avoirdupois. It now weighs TyL ozs. In other terms, its specific 

 gravity has been reduced from about 7.168 to 2.830, by lying 30 

 years in the ocean. 



(Note. — By calculation, if 18 ozs. be reduced to 7^0, 7.168 falls 

 to 2.832, which closely confirms the experiment.) 



The above facts were obtained in a conversation with Mr. Gordon, 

 the President of the Company, who kindly placed these specimens in 

 the Mint cabinet. 



Assay Office, U. S. Mint, October 16, 1845. 



N. B. To bring the dollars into a condition fit for deposit at the 

 Mint, the incrustation upon them, consisting of shelly and earthy 

 matter, combined with sulphuret of silver, is first removed. A con- 

 siderable quantity of this coating has been reduced into metallic silver 

 at the Mint, yielding 38 per cent, in silver. The crusts of black sul- 

 phuret, comparatively free from shell, yield 70 per cent. The aver- 

 age value of the dollars, with this taken into account, is about 94 

 cents. 



Whether the dollars would have suffered so much by the mere 

 action of sea-water, is open to inquiry. The loss in this instance is 

 clearly due to the attacks of sulphur, most probably from the gun- 

 powder. No muriate of silver was found in the analysis. 



Mr. C. M'Euen exhibited to the Society an engraved Re- 

 volving Table, intended to show approximately the time of the 

 meridian passage of a star. 



