IN METALLIC TUBES. 43 



therefore probable that this takes place in the metallic 

 tubes, though the, metal is not in the ftate of a calx, but 

 may be, as it were, fuper-faturated with phlogiflon. 

 When I opened one of the copper tubes in which this ex- 

 periment had been made, 1 found the metal exceedingly- 

 bright ; whereas had any phlogiflon been feparatcd from 

 it, it would have been covered with fcale, being reduced 

 to the ftate of calx. Whether the fame metallic tube 

 would continue to have the fame effe£t in this procefs, 

 or whether, when faturated to a maximum with phlo- 

 gifton, the mixture of air would have exploded in it, I 

 did not try ; feveral of the copper tubes, or the foder, 

 having melted before this could be afcertained. 



I alfo found that when 1 threw the focus of a burning 

 lens upon fome clean filings of copper in inflammable 

 air, much of the air difappeared ; having, no doubt, been 

 imbibed by the metal, which muft thereby have acquired 

 more phlogifton than naturally belonged to it. 



For the purpofe of thefe experiments I prepared a 

 mixture of one-third dephlogifticated and two-thirds in- 

 flammable air, each very pure, fuch as made the loudeft 

 explofions when a lighted candle was prefented to any 

 portion of it ; but neiiher in tubes of iron, copper, filver, 

 or gold, was there any exploiion at all, though as ftrong 

 a heat as they would bear without melting was con- 

 tinued ever fo long. As the quantity and flate of the 

 air after the experiments deferve fome attention, 1 fhall 

 recite fome of them. 



One meafure of the mixture above mentioned heated 

 in a copper tube was reduced to 0.45, and was wholly 

 phlogifticated. Another meafure of the fame mixture 

 expofed to heat ten minutes in a tube of filver was re- 

 duced to 0.73, and then exploded. Another meafure 

 expofed in a tube of gold was diminifhed about one-third, 

 and made a flight explolion afterwards. 



Fa 2. 0/ 



