368 
TRANSACTIONS OF THE PHARMACEUTICAL SOCIETY. 
from this, with a one-foot 
column in five minutes, was 
18^ ounces, equal to 0-247 
of an ounce, or about ten 
drops (grains) per square 
inch per minute. (The flow 
through the flannel previous¬ 
ly mentioned was nearly one 
hundred times faster per 
square inch per minute.) 
The glass tube of the block 
was now passed through, 
and secured to, a hole or 
short pipe in the bottom of 
a small cistern, after the manner shown in 
the larger woodcut. Forty-four feet of 
three-eighth composition metal gas-piping 
was now added to the glass-tube. The cis¬ 
tern being kept full of water, the metal 
tube was gradually lowered down the well 
of a staircase, forming a curve like the letter 
U, and thus filled with the water to the 
exclusion of every trace of air. This -was 
done, because in some previous trial expe¬ 
riments the presence of air in the small cen¬ 
tral cavity of the block was found to inter¬ 
fere with the hydrodynamic action, and to 
nearly reduce the rate of flow to what was 
set up by aerostatic pressure. Indeed, it 
may be well to state at once, that in order 
to remove this source of error altogether, 
even at lengths of the column at which the 
pressure on the interior of the filter was so 
reduced that several cubic inches of air 
came out of solution in the 'water at every 
experiment, the hole in the block was con¬ 
tinued quite through to the upper surface, 
a glass tube inserted into the upper orifice, and a glass flask filled with water 
fitted on to the tube by a cork. Any air now disengaged in the interior of a 
block rose up into the inverted flask, and thus the continued integrity of the 
column was secured (see the accompanying woodcut). On now lowering the 
open extremity of the long metal U tube, the following were the amounts of 
water obtained at different distances during a period of five minutes in every 
case. The hydrodynamic rate of flow and the rate of increase of aerostatic 
pressure are given for comparison. 
Hydrodynamic rate. 
Actual rate. 
Aerostatic proportions. 
At 3 
feet 
. . . 41 
ounces . 
. . 41 ounces 
. . . 41 ounces. 
6 
11 
. . . 58 
55 
. . 67 
55 
... 82 
55 
9 
11 
. . . 71 
55 * 
. . 93 
55 
. . .123 
55 
12 
5) 
. . . 82 
55 
. . 130 
55 
... 164 
55 
15 
>1 
. . . 91 
55 
. . 164 
55 
. . . 205 
55 
18 
11 
. . .100 
55 
. . 198 
55 
. . .246 
5 5 
24 
51 
. . .116 
5> • 
. . 230 
55 
. . .328 
5 5 
30 
15 
. . .130 
55 
. . 270 
55 
. . .410 
55 
36 
M 
. . . 142 
55 
. . 288 
55 
... 438 
55 
42 
55 
. . . 154 
55 
. . 301 
55 
... 438 
55 
