PROFESSOR GRAHAM ON THE MOTION OF GASES. 
585 
more than the numbers 1*209 and 1*214, in the two divisions of the scale; or 1 part 
in 242, a deviation which may be considered as within the errors of observation. 
The mixtures of carbonic acid and air have also the mean times of the pure gases. 
6. Effusion of mixtures containing Hydrogen. 
* [I was induced to examine the effusion of mixtures of hydrogen and other gases 
very minutely, in order to elucidate if possible certain singular peculiarities which 
were observed in the transpiration of these mixtures by tubes. A new plate E was 
employed, composed of thin platinum foil y^th of an inch in thickness, with a cir- 
cular aperture yg-oth of an inch in diameter, as measured by Mr. Powell by means 
of a micrometer. It was desirable to simplify the experiment at the same time by 
operating upon a constant volume of gas, measured before effusion, and drawn into 
an aspirator-jar which was maintained vacuous, or as nearly so as possible, by un- 
interrupted exhaustion. The gas was measured in a globular jar, to which more 
particular reference will be made hereafter. It contained 65 cubic inches between 
two marks, one upon each of its tubular axes, and was supported vertically over 
the water of a pneumatic trough. 
The little brass tube upon which the perforated plate is fixed (a. in fig. 5, Plate 
XXXIII.) was now made to screw upon the end of one of the stop-cocks, namely, 
L (fig. 1.), which is immediately attached to the aspirator-jar, and projected up- 
wards within the block tin tube H. The perforated plate was fixed to the end of its 
brass tube by means of soft solder. 
The results thus obtained I consider superior in value to those already detailed, 
from the longer periods of observation, the time for air generally amounting to 800 
or 900 seconds ; from the new plate being thinner and its aperture of a regular cir- 
cular form ; and from the greater simplicity of the conditions of the experiment, namely, 
the passage of the gases into a sustained vacuum under the whole atmospheric pressure. 
The series of experiments is divided into five sections, each containing the experi- 
ments of one day, to which the height of the barometer and the temperature are added. 
Two observations were made of the time of effusion in seconds for each gas, which 
are given under the columns of experiments I. and II., and the mean of the two ex- 
periments is added in a third column. This mean is expressed in the column which 
follows, with reference to the time of oxygen as 1. The additional column headed 
“ calculated times of mixtures, oxygen= I,” contains times of the mixtures, calculated 
from their specific gravities, being the square roots of the densities of the respective 
mixtures. The observed times of the hydrogen mixtures will be seen to correspond 
very closely with these calculated numbers, the maximum divergences not exceeding 
that of pure hydrogen itself. 
* The passages and tables in this paper, which are inclosed in brackets, as the following to p. 587, have 
been added during the progress of the paper through the press, and the date of the addition is in each case 
noted at the end of the last paragraph — S. H. C. 
4 G 
MDCCCXLVI. 
