CARBONIC ACID GAS EXPIRED FROM THE LUNGS AT DIF. PERIODS. 1 
chromate of lead were observed on the surface 
of the chalk. By mixing sub-nitrate of cop- 
per, with arseniate of copper, a double arse- 
niate of copper and ammonia, and of arseniate 
lime and ammonia is formed The re-action of 
bi-carbonate of soda upon gypsum gives ori- 
gin to carbonate of lime which crystallizes, 
sulphate of soda remainingin solution. 
A supplementary chapter is appended, 
containing a short outline of the interesting 
electro-chemical researches of Dr. Faraday. 
ON RESPIRATION. 
BY THOMAS THOMSON. M. D., F. R. 6., t,. 
AND E., &C, 
Uegius Professor of Che^nistrij in the Uni- 
versity of Glasgoiv^ 
When the experiments on respiration were 
made by Lavoisier, Goodwin, Menzies, Davy, 
&c., towards the end of the last century, it 
seems to have been the generally received 
opinion, that every individual by inspiring the 
air into his lungs, produces the very same 
change upon it. At least, the conclusions 
respecting respiration to be met with in Phy- 
siological and Chemical books, depend for their 
accuracy, upon this assumption. Nothing, 
however, can be farther from the truth. The 
chemical changes produced in air by respira- 
tion, vary in their extent, not only in different 
individuals, but even in the same individual at 
different times ; and that to such an extent, 
that if we analyze air thrown out of the lungs 
at different times, we find the quantity of 
carbonic acid, sometimes not to exceed two 
per cent, and at other times to amount to 
more than seven per cent. Dr. A. Fyfe and 
Dr. Prout have shown many years ago, that an 
alteration is produced in the quantity of car- 
bonic acid in the air expired, by the mode of 
living of the individual : that when the con- 
stitution is affected by mercury, the propor- 
tion of that gas in the air expired is diminished 
Rnd that it is diminished also by nitric acid, 
by spirits, and by a vegetable diet. But I 
have found that the most unexpected altera- 
tions are observable in the same individual, 
though he be in perfect health, and though he 
make no sensible alteration in his mode of 
living. 
During the course of the month of May, 
1832, 1 analyzed air from my own lungs on ten 
consecutive days, between eleven and twelve 
o’clock each day. Before stating the results, 
it may be proper to mention the method of 
analysis employed. I procured a glass tube, 
capable of holding about three cubic inches 
of air, and about half an inch in diameter. It 
was shut at one end and open at the other. 
This tube being filled with mercury, and 
placed inverted on a mercurial trough, I in- 
troduced into it about two and a-half cubic 
inches of air from my lungs, taking care, in 
the first place, by making half an expiration 
through a narrow glass tube, to expel all the 
common air from the trachea and mouth, and 
also from the tube, by which it was conveyed to 
the eudiometer The surface of the mer- 
cury in the tube was then marked by tying 
round in a sewing thread, and the whole was 
left till the air ceased to contract. Then a 
quantity of moderately strong potash ley was 
introduced, and the whole was left untouched 
for twenty-four hours. The diminution of 
bulk of the air was then carefully marked, by 
tying a sewing thread rou.id the tube at tlio* 
new surface of the mercury. I then filled 
the tube with mercury, up to each of the 
places marked by the sewing threads, and 
weighed each portion of mercury. The dif- 
ference between the two weights, gave the 
diminution of bulk sustained by the air, by 
the absorption of its carbonic acid, I then 
calculated, what the bulk of the air and of the 
carbonic acid gas absorbed would have been, 
at the mean pressure and temperature ; making 
allowance for any change in the height of tho 
barometer and thermometer, which took place 
during the interval, I ought to observe, 
however, that during the ten days of these 
experiments, both the barometer and the 
thermometer were tolerably steady. 
The following table exhibits the volume, of 
carbonic aci4 gas, in 100 parts of the air ex- 
pired from my lungs during each of the ten 
days, at 11 o’clock a. m. : — 
CARBONIC ACID. 
1 . . 4'()4 per cent, 
2 . . 4'70 
3 . . 6-07 
4 .. 3’*27 ,, 
5 .. 5-26 
CARBONIC ACID. 
6 . . 2 O.o per cent. 
7 .. 2 .39 
8 .. 3 85 
9 .. 3.05 
10 .. 7.16 
I was not a little surprised at these re- 
sults: the differences being so much greater 
than I had anticipated. The mean of the 
whole is 4‘24 per cent., which, therefore, I 
am disposed to consider as representing the 
mean quantity of carbonic acid gas, contained 
in iOO volumes of air expired from my lungs. 
I was naturally induced to examine the air 
from the lungs of several other persons, in 
order to see whether there would be the same 
difference in theirs as I had observed with 
respect to myself. The gentlemen whose 
breathing was examined, W'ere chiefly those 
who were occupied with practical chemistry 
in my laboratory. The following table exhibits 
the results obtained : — 
CARBONIC ACID. 
Mr. Thomas Thomson, (aged 14) 3-06 per 
cent. Ditto, next day, 3.61, Mr. .1 . Calqu- 
houn (aged 18) 3.09 Mr. Farrest (aged 18) 
2.10 ditto next day 5.19 Mr. Coverdale 
2-o4 ditto, next day, l-7i Mr. Cargill, 4-68 
Mr. Bruce, 5-46 Dr. Duncan, 6. 1 7 Dr. Short, 
6-85 Mr. Frazer, 7-08. 
I prevailed upon two ladies to allow me to 
examine the air from their lungs. The first 
was an unmarried lady about seventeen years 
of age ; the second a married lady, aged 
about 30. The results were as follows 
First lady . . 2-35 1 Second lady . . 4-06 
The diversity here is fully as great as in my 
own case, but the mean of the whole does not 
differ much from that of my own. I am dis- 
posed, therefore, to infer from these trials, 
that the average volume of carbonic acid gas, 
in 100 volumes of air, expired from the lungs 
at 11 o’clock A. M. is 4-24. 
