VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 211 



3 hours and a half. When water was substituted instead of mercury, air issued 

 slowly, and as if with difficulty, under a pressure of 5 inches. When only -^ an 

 inch was left over the mouth of the tube, small bubbles ascended freely. During 

 a considerable time I counted 4 slowly between each of these bubbles. I did not 

 collect above 3 oz. measures of air, and this contained carbonic acid. It was past 



4 o'clock when the apparatus ceased to be air-tight, and the fire had been kept as 

 strong as possible. The iron was most completely fused. There was a good 

 deal of revived lead within the retort ; there were also many globules in the neck. 

 Probably some broken flint glass had been added to the usual materials for crown 

 glass ; I cannot otherwise account for the appearance of the lead here. In the 

 last experiment the lead of the flint glass had been revived. 



Exper. 5. Two ounces of the same iron, immediately on being taken out of a 

 retort, in which they had been kept, at a red heat, for about an hour and a half, 

 and which were therefore as free from water as iron can easily be procured, were 

 put into an earthen tube, unglazed, and closed at one end. This tube was dis- 

 posed as in expt. 2, only the end of the glass tube was immersed in mercury, in- 

 stead of water. But air did not now come over so soon as in any former instance. 

 When the fire was raised to its full force, exactly the same amusing variety of 

 appearances took place as in the last experiment. Under the pressure of half an 

 inch of mercury, not a particle of air was discharged ; but the moment the 

 pressure was diminished to a small fraction of an inch, the bubbles succeeded each 

 other pretty quickly ; and so on repeatedly. On lowering the surface of the 

 mercury, and pouring some water on it, I received more than 2 oz. measures of 

 air, which, by the test of lime-water, seemed to contain a vestige of carbonic 

 acid, but it was too minute to be appreciated. This experiment with the air was 

 made after a strong white heat had been kept up for 3 hours. Soon afterwards 

 the bubbles ceased ; but we could not then, nor on examination of the apparatus 

 when cold, discover any failure. The fire was still kept up for 3 hours. The 

 tube must have been exposed to a strong white heat 7 hours in all. The iron 

 had lost 1 1 grs. in weight. Only about one half had been thoroughly fused. The 

 surface of 2 lumps, that had not been fused, had the close texture, and silvery 

 appearance, of malleable iron. The thin edges yielded to the stroke of the ham- 

 mer, and a gentleman, perfectly conversant in the nature of iron, agreed with 

 me, that it had all the characters of malleable iron. 



Exper. 6. Thirty-one grains of artificial plumbago, in shining flakes from the 

 iron works, were exposed in a small retort to a strong heat, for 6 hours, in the 

 same pneumatic apparatus. It was difficult to separate, even by the help of the 

 magnet, all the intimately mixed particles of iron, and there were also a few par- 

 ticles of coak incorporated with the plumbago. Air, of an explosive inflammable 

 kind, was extricated, and rose freely through 5 inches of mercury. We had 



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