AND OTHEE PHENOMENA OE EESPIEATION. 633 
A mask (A) is worn of a capacity only just large enough to receive the nose, lips, and 
chm, and the apertures of the entrance and exit tubes. The part which sustains the 
tubes (A 2) and the valves is made of brass, to the free edges of which is soldered sheet- 
lead of sufficient thickness to remain fixed upon the features when it has been well 
moulded to them (A 1), and to prevent the entrance of air except through the entrance- 
tube. Elastic bands are suitably attached to it so as to bind it upon the head, when the 
hands must be left ffiee for other purposes. The entrance-tube is connected with the 
spmometer by vulcanized caoutchouc tubing, and during the insphation of the air the 
mdex of the spu’ometer (B 1} registers the quantity from 1 to 1 million cubic inches, 
ihe exit-tube leads to the analytical apparatus, and is connected with it by vulcanized 
tubmg. There are valves suitably arranged to prevent a retrograde current, and so light 
that they do not ofi'er any important amount of resistance to the current of the expired air. 
The analytical apparatus consists of — 
1st. A Woulfe’s bottle (C), of the capacity of 70 cubic inches, which is filled with 
pieces of pumice-stone moistened with sulphuric acid. To the bottom of this the 
cuiTent is directed, and in it the vapour is abstracted from the expired air. 
2nd. A gutta-percha box (D), consisting of a series of chambers, each fths of an inch 
m depth, and offering a total superficies of 700 inches. The chambers are imperfectly 
su divided by partitions (E) into compartments of 2 inches wide, and so arranged that 
the column of am must traverse the several compartments in each chamber, and each 
chamber m succession from the bottom to the top of the box. Hence a column of air, 
2 Indies wide X fths of an inch deep, is dhected over an area of 700 inches. This area 
IS occupied by a solution of caustic potash of sp. gr. 1-27, which is introduced into each 
chamber separately, and which, through fissures in the partitions of the compartments, 
passes freely over the whole surface of each chamber. By this arrangement all the car- 
bonic acid IS abstracted Tilth the rapidity of ordinary expiration; and 30 fiuid ounces of 
the solution was found by experiment to abstract the whole carbonic acid up to 600 grains. 
(It 11111 be obseried that the air is not passed into, but only over caustic potash.) 
3rd. A second drying apparatus (C), similar to the ffi-st one, to abstract the vapour 
which had been carried off from the solution of potash. 
4th. A test of baryta water, over which the current was made finally to pass. 
At the conclusion of each inquiry, the increase in weight of the potash-box (H), and 
the second drying apparatus (C), gave the amount of carbonic acid abstracted ; and this 
was determined by the aid of one of Oertlixg’s balances (F), constructed to weigh, with 
great caie, to the xoolh of a grain, ivith 7 lbs. in each pan ; but it was not employed to 
infficate less than the ^J^th of a grain in the large quantity of carbonic acid collected. 
he apertures of the tubes throughout the apparatus had an area equal to that of the 
rac ea, so as to offer the least possible resistance to the current of air; a pressure of -j^ths 
o an inch of a column of water sufficed to move the spirometer, and an adverse pressure 
a out half that amount was offered to expiration. By a series of experiments, I deter- 
mined the extent to which the drying and carbonic-acid-abstracting apparatus were per- 
ect y efficient ; and care was always taken to keep much within those limits. Several 
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