in the different Kinds of Gas, and in Fliads. 23 



an hour and a half the phosphorescence of the wood had 

 for the most part ceased. At the end of 24 hours I there- 

 fore introduced another piece of wood, which exhibited the 

 same phaenomena as the preceding. This operation was 

 often repeated in the same gas. When the luniiuous ap- 

 pearance of the wood became weak, it recovered nearly its 

 original splendour, in the course of a few minutes, on 

 placing it in atmospheric air. I tried the remaining gas in 

 the eudiometer, but could observe no decrease ; which proves 

 that the gas had remained free from any mixture of oxygen 

 gas. 



When a piece of luminous phosphorus is placed near the 

 wood, it is difficult to determine the moment when the 

 light of the latter becomes entirely extinct : for I found 

 that the phosphorus generally remains luminovis a consi- 

 derable time longer than the wood, and even after its light 

 is extinguished a somewhat luminous vapour arises; so that 

 on account of this vapour it is not easy to ascertain w'hen 

 the phosphorescence of the w^ood ceases. It is equally dif- 

 ficult to observe, whether, on the admission of oxygen gas 

 to azotic gas containing wood and phosphorus, the light of 

 which is extinct, both these substances begin to be luminous 

 at the same time, or not ; for at first the gas is entirely illu- 

 minated by the luminous vapour ; and besides this, the 

 surface of the rotten wood becomes entirely luminous, in 

 consequence of the ])hosphoric particles deposited on it ; 

 and hence it is difficult to determine whether the light pro- 

 ceeds from itself or from these particles. I often found such 

 pieces of wood when taken out entirely penetrated with 

 particles of phosphorus. This observation may be of utility 

 to the future observer. 



Experiment V. 



I filled a common bell glass with phosphorated azotic gas, 

 in which a considerable quantity of phosphorus had re- 

 mained several weeks, at the temperature of from 1 4 to 24° 

 of Reaumur, and in which fresh phosphorus neither eva- 

 porated nor became luminous. A piece of wood placed in 

 this gas continued at first luminous, without any decrease of 

 intensity. In about half an hour however its light became 

 weaker, and in an hour entirely disappeared. Next evening 

 I introduced into the same gas a fresh piece of wood, and 

 observed the same phaenomena. On introducing more phos- 

 phorus it emitted as little light as before, 



B 4 Experiment 



