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D. A. Kreider—Forms of Laboratory Apparatus. 133 
small space between the tube and the rubber when the latter is 
loosely drawn over it: but in order to work easily, should be 
long enough to permit a slit of about a centimeter’s length to 
close tightly, which will require it to be about twice the length 
of the slit. A slit one centimeter long will be found to open 
under very slight pressure, and to accomplish its purpose it is 
only required to close sufficiently for the external pressure to 
force the rubber against the opening in the tube. This open- 
ing should be carefully rounded and a little higher rather than 
any lower than the surrounding glass, and is better made before 
sealing the end, in order to keep the tube perfectly straight. 
The rubber should fit tightly about the larger parts of the 
glass tube and be put on with care to have the smoothly cut 
slit straight and loose enough to close tightly. If the slit is 
placed about 90° from the opening in the tube, sufficient space 
will remain to permit the escape of the gas or liquid, but the 
moment the pressure outside becomes greater than that within, 
the rubber will be pressed tightly over this opening and thus 
a return made impossible. When dry the valve was found 
not to resist high pressure perfectly ; but when wet, or better 
when both glass and rubber, including the slit, were moistened 
with glycerin, a column of mereury 730™" high was held for 
several days without changing more than the barometer. The 
valve thus lubricated with glycerin when used as a protection 
in an ammonia wash-bottle, will prevent absolutely the access 
of ammonia to the mouth, and if made according to the direc- 
tions will act with very little pressure. Placed in the connec- 
tion between the vacuum flask and water pump ordinarily used 
in filtration, it has been found a valuable check on the valve of 
the pump, and when the latter was impotent this device pre- 
vented any water being drawn into the filtrate. In a process 
soon to be published, in which a partial vacuum is used, this 
valve holds the vacuum in continual readiness and adds greatly 
to the convenience of the process. 
Force Pump.—By adjusting two of the valves 
just described to the opposite extremities of a T- 
tube, with the horizontal limb enlarged or sealed to 
a larger tube so as to permit the attachment of a 
large and stout piece of rubber tubing closed at one 
end, as shown in fig. 3, a convenient and powerful 
little foree pump is obtained. A small bore, stout 
T-tube is cut off short at the two ends at right 
angles to one another: to one is sealed a tube just 
large enough to permit the insertion of a valve; to 
the other, a large tapering tube, slightly lipped so 
as to hold a piece of rubber tubing firmly and allow 
of tying the latter if necessary. Of the third end 
of the tube, a valve like that shown in fig. 2 is made. 
The compressing rubber should not be of greater 
