PROFESSOR GRAHAM ON THE MOTION OF GASES. 
359 
The times for air being 460 and 459 seconds, those of carbonic acid were 381 and 
381 seconds, and those of protoxide of nitrogen (NO) 380 and 380 seconds; ther- 
mometer 56°, barometer 29 674. 
Transpiration time of carbonic acid 0’7448 
Transpiration time of nitrous oxide 0’7429 
results which illustrate the identity in transpiration rate of these two gases, which 
have also the same specific gravity, and appear to correspond remarkably in several 
other physical properties. 
The difference of resistance to the passage of a gas offered by the various capillary 
tubes already used is certainly considerable ; the resistance for equal lengths of tube 
being in round numbers fifty times greater in the new capillaries K and M, than in 
the old capillaries E and H. But large as is this range, in which a remarkable uni- 
formity of transpiration rate of the gases has been observed, it may still be much 
extended. The capillaries of extreme resistance to which I shall now refer, have 
great advantages over the others already described, and form the instruments which 
I would recommend for the further study of the laws of transpiration. 
A thermometer tube of the finest cylindrical bore being selected, a portion of about 
8 inches is taken, and being progressively heated and softened at the lamp, is crushed 
up into a length of 1 inch or less, which can be done without obliterating the cavity. 
The cylindrical mass is then, while still soft, drawn out into a tube of ten or twelve 
times its original length. A thin and extremely fine capillary tube is thus obtained, 
which is much more regular in bore than might be expected from the description of 
its preparation. It is convenient to divide the rod, which is less in diameter than a 
fine straw, into lengths of 4^ inches, and to seal immediately the open extremities of 
each piece. A transpiration capillary was formed of a bundle of thirty of these little 
rods, which were placed together within a short glass tube, as a case, of about 3 ^ inches 
in length and half an inch in diameter; so that the ends of the rods projected at both 
ends of the tube. The rods were fixed within the tube by stucco, which was dried and 
afterwards, while warm, soaked in melted bees’-wax. These arrangements being en- 
tirely completed, and the bundle proved to be impervious to air, the ends of the rods 
were now broken off, and the tubes thus opened. The transpiration instrument P 
consisted of a bundle of thirty such capillary tubes, each about 4 inches in length. 
Each end of the solid cylinder was connected with a block-tin tube of the same dia- 
meter by means of a thick vulcanized caoutchouc adopter. One of these tin tubes 
was connected with the aspirator-jar, or left open to the air, and the other connected 
with the receiver containing the gas to be transpired. 
The mode of conducting the experiment was further changed. Instead of drawing 
the gas through the capillaries into an exhausted receiver or vacuum, the gas was 
compressed in a stout metallic receiver or condenser, provided with a mercurial 
pressure gauge, by which the elasticity of the gas within could be observed*. This 
* Phil. Trans. 1846, Plate XXXIII. fig. 3. 
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