522 



APPARATUS FOIl 



expected no change of result to take place, whether 

 the surface were black or resplendent. 



Experiment 29. — Let a tube be taken of the 

 greatest length that will admit the flame to pass en 

 tirely through it. Add to this as much more tube 

 as will prevent the flame appearing at the bottom : 

 try if, by discharging a grain of the powder, a piece 

 of paper tied over the under part will be torn ; if it 

 be not torn, then heat as much of the tube as can 

 be conveniently done, and discharge as before the 

 same quantity of powder ; and observe if the flame 

 be now forced through a longer tube than it was be- 

 fore, when the tube was cold. 



Should this last experiment prove to us, " that 

 the flame will pass through a longer hot tube than 

 it will through a cold one," then we have the possi- 

 bility of the calorie existing in a free independent 

 state, still more strikingly shewn. We have here 

 taken a tube so long that the air cannot pass to the 

 bottom of it ; the air stops merely because the 

 power of its motion is exhausted, by the opposition 

 of the air in the tube ; there is no attraction of ab- 

 sorption or any other nature exerted, which could 

 be weakened by applying heat. But, on the, o^her, 

 hand, all matter has a tendency to receive caloric, 

 and the lower the temperature is the more is this 

 tendency encreased ; therefore, when a tube which, 

 at a low temperature, does not admit the flame to. 



