210 PHILOSOPHICAL TRANSACTIONS. [anNO 1792. 



much more slowly ; during a considerable part of this experiment you might 

 count 12 slowly between every air-bubble. When the utmost power of the fur- 

 nace had been exerted for 3 hours, a phenomenon occurred which produced some 

 surprize in every person present ; and there were several who had been abundantly 

 accustomed both to chemical and metallurgical operations. A considerable ab- 

 sorption took place, and for about half an hour, it was necessary to blow air up 

 the glass tube, to prevent the water from rising into contact with the iron. It 

 afterwards appeared that the lead of the glazing was revived, which sufficiently 

 explains the absorption. 



586 grs. only of the iron had been completely fused. The surface of 2 of the 

 unmelted lumps was curiously covered with numerous small blisters of metallic 

 lead. About 7 hours after the fire was first kindled, it was discovered that the 

 apparatus had failed. I had examined the air that came over immediately before 

 this accident, both by means of lime-water, and milk of lime, without discover- 

 ing any vestige of carbonic air. The iron weighed altogether 3 grs. more than at 

 first. But the adhering lead, and a quantity of lead also which was incorporated 

 with the iron, concealed a real, and probably a considerable, loss of weight. The 

 phenomena it exhibited, when put into weak vitriolic acid, and the vitriolated lead 

 which was formed, indicated the presence of this metal in all the superficial parts 

 of the mass. When it had been kept some time in vinegar, it dissolved readily 

 enough in vitriolic acid at first, but the solution soon ceased, or became very 

 slow. 



Exper. 3. A coated flint glass retort was employed in this instance. The ap- 

 paratus resisted a strong heat for 2 hours; and air, of the heavy inflammable kind, 

 came constantly over. 



Exper. 4. A coated retort of crown glass, containing 6 oz. Troy of the same 

 iron, was placed on a crucible nearly full of sand, and disposed as in the former 

 experiments. I now wished to measure the quantity of the air, and I therefore 

 determined to receive it in mercury. It would have been in vain to attempt this 

 in water, on account of the carbonic acid air. About 12 o'clock the retort was 

 judged to be of a dull red heat, and inflammable air came over. The orifice of 

 the transmitting glass tube was now covered to the depth of -i- an inch with mercury 

 when the discharge of air instantly ceased : the lute seemed entire. Some of the 

 mercury being removed, so as to leave just enough to cover the mouth of the 

 tube, immediately the air issued again in bubbles, a proof that the apparatus was 

 entire. The mercury was poured into the trough again, and in an instant there 

 was a cessation of air. The mouth of the tube being uncovered, and a lighted 

 paper applied, a blue flame appeared, and continued to burn, so great was the 

 quantity of air discharged. The orifice of the tube was -^i\'\ of an inch in dia- 

 meter. We found that this constant flame could be produced at any time during 



