622 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



tion above the horizon. Between Dec. 3 and 10 the comet was entirely effaced 

 by the increased light of the moon. On the 10th, the moon being in the 

 horizon did not obliterate stars of the 8th or 9th magnitude ; but he could not 

 find the comet. 



The following observations were made by Mr. John Goodricke. 



Dates. 



1783 

 Novemb. 24 

 28 



Apparent 

 time. 



h. m. 

 8 16' 

 6 8j 



R. A. 



36 32 57 

 33 20 



North de- 

 clination 



9 30| 

 14 161 



Longitude. 



31 



Latitude. 



1 42i s. 

 52| n. 



XXXV11. Experiments on Mixing Gold with Tin.* By Mr. Stanesby Alchorne, 



of the Mint. p. 463. 



It is a generally received opinion among metallurgists, that tin has a property 

 of destroying the ductility of gold, on being melted with it, even in very small 

 quantities. The late Dr. Lewis, in his Phil. Commerce of Arts, p. 85, has 

 well expressed the sense of most writers on this subject, in the following words : 

 " The most minute proportion of tin and lead," says he, " and even the vapours 

 which rise from them in the fire, though not sufficient to add to the gold any 

 weight sensible in the tenderest balance, make it so brittle that it flies in pieces 

 under the hammer." Divers circumstances, however, says Mr. A. long since 

 induced me to disbelieve the fact ; but these, having chiefly arisen from small 

 experiments, did not seem to warrant any general conclusion. But a late 

 public occasion, which led me to various trials of mixing these metals together, 

 in different proportions, and in sufficiently large quantities, has put the matter 

 out of doubt ; and shown me, that tin, in small quantity at least, may be added 

 to gold, either pure or alloyed, without producing any other effect than what 

 might easily be conceived, a priori, from the different texture of the two metals! 

 In confirmation of which, I beg leave to lay some of the experiments before you. 



Exper. 1. Sixty Troy grains of pure tin were stirred into 12 oz. of refined 

 gold, in fusion ; and the mixture was then cast into a mould of sand, producing 

 a flat bar, 1 inch wide, and \ of an inch thick. The bar appeared sound and 

 good, suffered flatting under the hammer, drawing several times between a large 

 pair of steel rollers, and cutting into circular pieces, of near an inch diameter, 

 which bore stamping in the money-press, by the usual stroke, without showing 

 the least sign of brittleness ; or rather with much the same ductility as pure gold. 



Exper. 2. Ninety grains of like tin were added to 12 oz. of fine gold, stirred, 

 and cast as above. The bar produced was scarcely distinguishable from the 

 former, and bore all the operations, as before-mentioned, quite as well. 



* This subject has been further prosecuted by Mr. Hatchett in the Philos. Trans, for 1783. 



