280 MESSRS. ALLEN AND PEPYS ON THE RESPIRATION OF BIRDS. 
At the end of the first twelve minutes we noticed a good deal of dew upon 
the glass opposite to the head of the pigeon ; at first we gave a fresh supply of 
air every five minutes, but at the end of 31 minutes the bird appearing a little 
uneasy, we supplied him every four minutes ; and at the close of the experi- 
ment, which lasted 69 minutes, he did not appear the worse for it. We thought 
that the register indicated a slight diminution of volume during the time that 
the bird was uneasy ; the air respired was examined as usual, with lime water 
in the eudiometer with an elastic bottle, for carbonic acid, and with green sul- 
phate of iron saturated with nitrous gas, for oxygen. 
State of the air before the experiment : Atmospheric air 587 cubic inches, 
consisting of 123 oxygen, 464 azote. 
State of the air after the experiment: 587 cubic inches, consisting of 35.80. 
carb. acid, 87-52 oxyg., 462.67 azote. 35.80 4- 69 = .52 cubic inches per minute. 
Thus it appears that the bird produced about half a cubic inch of carbonic 
acid per minute ; and as the volume of oxygen consumed is always equal to 
the volume of carbonic acid produced, the 35.80 being added to the oxygen 
found after the experiment, or 87-52 cubic inches, very nearly corresponds with 
the 123 contained in the common air before the experiment. Now as 100 
cubic inches of carbonic acid contains 12.82 grains of carbon, the 35.80 cubic 
inches produced by the bird in 69 minutes must contain 4.59 grains of carbon, 
or nearly at the rate of 96 grains in 24 hours. 
The azote before the experiment was 464 cubic inches ; after the experiment 
462.67 : the difference is only 1.33, or little more than a cubic inch, which loss 
might have happened during the time the bird was uneasy ; and we may fairly 
conclude that when birds respire atmospheric air, the only change in the air is, 
the conversion of a part of its oxygen into a corresponding portion of carbonic 
acid gas. 
First experiment with oxygen gas. 
The oxygen was made from chlorate of potash, and being examined as usual 
with the eudiometer, it was found to contain 2 per cent of azote. 
The barom. being 29.5, the therm. 51°, we placed the pigeon in the inter- 
mediate glass vessel in the same situation as in the former experiment. 
