238 M. Marcet on the Changes which the Atmosphere 



the thermometer being at 72°. They were then exposed to the 

 light of day, though not in the sun's rays, for ten hours. At 

 the expiration of this time, the volume of air had augmented to 

 87.33 cubic feet. The following is its analysis : — The receiver 

 inclosed, before the experiment, of nitrogen 28.12, of oxygen 

 7.46, = 35.58 ; after the experiment, of nitrogen 28.06, of oxy- 

 gen .24, carbonic acid 9.02, = 37.32. 



In this instance 7.22 cubic feet of oxygen had disappeared, 

 and gone to the formation of the same volume of carbonic acid 

 gas. The mushrooms altogether had disengaged 2.4 inches of 

 carbonic acid from all the plants. 



The preceding experiments having been repeated during 

 twelve hours of the night, gave a result somewhat different. 

 The following are the details : — The receiver inclosed, before 

 the experiment, of nitrogen 28.12, of oxygen 7.46, — 35.58 ; 

 after the experiment, of nitrogen 28.12, of oxygen .73, carbonic 

 acid 8.73, - 37.58. 



It is worthy of attention, that in this instance the mushrooms 

 appear to have commenced the evolution of the carbonic acid 

 before having absorbed the whole, or the entire whole, of the 

 oxygen of the air, as had occurred in the former experiments, 

 which were conducted during the day-time. 



This experiment was a third time repeated, with two plants 

 of the species Agaricus campestris, together weighing 120 

 grains. They were first kept for twelve hours in a room, the 

 temperature of which varied from 65° to 68° Fahr. ; and were 

 then placed under a receiver, containing 29.17 cubic feet of air, 

 just at the time they were beginning to give out a distinct 

 odour, the first sign of decomposition. At the end of twelve 

 hours, the air of the receiver, the volume of which had not sen- 

 sibly altered, being subjected to analysis, was found to be com- 

 posed of carbonic acid 2.04, of oxygen 3*88, and of nitrogen 

 23.25, together 29.17. From this experiment it will be mani- 

 fest that the mushrooms which had been removed for many 

 hours from the earth, and which were on the eve of putrefac- 

 tion, produced less carbonic acid than those of the same kind 

 which were perfectly fresh ; an additional reason for presuming 

 that the considerable absorption of oxygen and disengagement 

 of carbonic acid which we have noticed as occurring in the pre- 



