for Measuring the Expansions of Solids, Sfc. 277 



carefully lifted out and set apart to cool. Its surface was per- 

 fectly clean, only a few small globules adhering to it, which 

 were easily removed. I may here I'emark, that stirrers of the 

 black-lead earthenware are constantly used at the Mint for 

 agitating the melted gold. The arc measured from this ex- 

 periment was 6° 10', equivalent to an expansion of '0537. 

 Temperature of the air about 65°. 



Exp. 9. The register III. was fitted with the iron bar, and 

 also heated to a dull red. The temperature of the melted 

 gold was prevented from rising by constant feeding with the 

 pieces; the crucible being never left without some portion 

 unmelted. It was then plunged beneath the surface of the 

 metal as in the preceding experiment, and held in that situa- 

 tion for ten minutes. The arc measured was 9" 2', indicating 

 an expansion of •0787. 



Exp. 10. The rates of expansion of the two last registers 

 were determined by boiling them for ten minutes each in 

 mercury. The results were as follow : 



Arc. Expansion. 



II. with the platinum bar l°-50 = -0159 



III. with the iron bar 2°-38 = -0229 



Exp. 1 1. About 50lbs. of pure silver were melted in a black- 

 lead pot: a little scum floated upon the surface, which ap- 

 peared at first like drops of oil upon a basin of water. I was 

 afterwards informed that the metal had been refined with nitre, 

 and the dross was owing to the action of a little remaining 

 potash upon the crucible. Two registers had been prepared 

 for the platinum and iron bars; but the observations were 

 lost from the same action upon their substance. They were so 

 deeply corroded in a line which corresponded with the level 

 of the fluid metal, as to render it impossible to apply the scale, 

 with any certainty, to their surfaces. 



Exp>. 12. Two new registers were selected, whose rate of 

 expansion was found by boiling in mercury to be equal ; the 

 arc in both cases being with the platinum bar 1° 20' = "01 16. 

 They were marked IV. and V. 



IV. was adjusted with the platinum bar. An ingot of silver, 

 which had been refined by cupellation, weighing about 35lbs., 

 was jilaced in a black-lead crucible in a wind-furnace. When 

 somewhat more than three-fourths were melted, the register, 

 previously heated to a dull red, was plunged into it as before, 

 and held down for ten minutes. When lifted out, its surface 

 was found perfectly good, and the few adhering globules of 

 metal were easily removed. When cool, the scale was ap))lied, 

 and the arc found to be \" 10' = expansion '0363. Tem- 

 perature of the air 65 '. 



Exp. 13. 



