238 Of a Suction and Forcing Air Pump. 
that this mode of opening valves, if unassisted, always allows a small 
portion of condensed air to remain in that portion of the chamber 
and of the passage leading to the valve, which the piston cannot be 
made to occupy entirely; This disadvantage is diminished in the 
case of the valves which Iam describing. A stem proceeding from 
each valve enters the chambers so far, as that the piston cannot 
finish the stroke without coming in contact with the stem, and mov- 
ing the valve sufficiently to allow the air to escape, without suffer- 
ing any resistance from the valve and its spring. 
The means by which the apertures of the suction valves commu- 
nicate with a valve cock A, and may be made to communicate with 
the receiver through the pipe P, have been explained. By like 
means the communication, existing between the apertures of the 
valves of efflux and a valve cock G, may be extended from this 
valve cock to any receiver. In fact, it is only necessary to vary the 
situation or number of the pipes, by which communications with the 
chamber are effected, in order to cause the apparatus to perform 
the part of an air pump, a condenser, or both. When employed to 
transfer air, it would be more correctly designated as a forcing air 
pump, than as a condenser. : 
_ The disk of brass in front of the pump, serves as an air pump 
plate, when connected with the pump by means of the pipe P, as 
represented in the drawing. It is supported on a hollow brass cylin- 
der, furnished with valve cocks as at K L, in order to allow various 
experiments to be performed by means of the tube in the axis, sur- 
mounted by acup of copper. The tube being open at the lower 
end, the cup is accessible to an incandescent iron. ‘The contrivance 
facilitates the exposure of substances to heat, either in vacuo, or in 
any gas. When boric acid and potassium are thus heated, boron is 
evolved. By means of a similar arrangement, heating chloride of 
calcium with potassium, I obtained a potassuret of calcium, which 
decomposed water and yielded a solution which was rendered milky 
by carbonic acid. 
When a glass globe of fifteen gallons is exhausted over this plate, 
and filled with oxygen gas, phosphorus having been previously pla- 
ced in the copper cup, on heating the phosphorus, a combustion en- 
sues of transcendent splendor. 
For this and other experiments, the hollow cylinder, which sup- 
ports the air pump plate, may be screwed into a hole in a table and 
placed at any convenient distance from the air pump. With this 
view, there is a conical screw cut upon the lower end of the cylinder. 
