244 MEASUREMENT OF HIGH TEMPERATURES. [bull. 54 
rubber hose at P, enables the observer to let the mercury flow int 
the receiver B from above by closing the stop-cock D. As this i 
the special feature of the present apparatus, and is essential for tab 
maintenance of constant pressure, I will describe it further. Suppos 
the Mariotte flask A to be hoisted in and fixed in the high position 
suppose the receiver B filled with air, and communication with th 
atmosphere and with the capillary tubes to be shut off, moreover, tb< 
stop cocks G and D closed. If now G be opened, mercury will flov 
from A to B through the hose and the lateral tube P Q. The head o 
mercury urging the influx will be the difference in height between ^ 
(the point of influx) and the lower end of the tube d in the Mariotte 
flask A. The flow will continue until the manometer _K registers thi 
equivalent pressure. If, now, the stop-cock K of the capillaries b< 
opened, the air from B will be very slowly discharged into the atinos 
phere and the mercury from A will slowly flow into the receiver B, en 
tering it from above in such a way that the pressure is maintained com 
stant throughout the course of the experiment; for the head of mer 
cury between Q and the Mariotte level remains unchanged until B ii 
quite filled, and the pressure value of the head is read off on the ma 
nometer B. Special care, however, must be taken with the construe 
tion of the Mariotte flask; for inasmuch as the flow from such a flasii, 
is necessarily intermittent, the period of jntermittence must be reducec 
to the smallest possible amount by compelling the air to enter m 
through d in very small bubbles. The lower end of the tube d is there 
fore drawn out into a capillary of, say, 0.05 cm diameter, which is grounc 
off obliquely in the usual way. It is still better to let the lower par 
of d end in a series of capillary platinum tubes, all cut off" obliquely 
with their open mouths nearly in the same horizontal plane. Air thus 
enters A in a spray of fine bubbles, and the internal ttence seen at R 
even in the most unfavorable cases of extremely slow efflux of gas ou 
of B, is reduced to 0.01 cm and less. 
The air in B enters the capillary tube through the stop-cock K. as ha: 
been said. The capillary platinum tube itself is shown at /, and h 
wound in form of a truncated cone, so as to be uniformly heated bj 
the adjustable burner n immediately below it, the gases of which an 
carried off by the adjustable chimney L. In other words, the helix o: 
the platinum capillary tube is so wound as to lie quite within the zone 
of fusion of the Bunsen burner. The outer end of the tube /commit 
nicates directly with the air. The other end is soldered into a lateral' 
arm of the tube K by means of resinous cement. In order to keep the 
joint cold and the inner end of the capillary at .a known temperature 
a rapid current of cold water from the hydrant flows through the cylin- 
drical sheet-iron box w, which surrounds the joint. 
Apparatus for constant pressure. — This form of apparatus was used in 
the earlier experiments, and the results obtained by means of it, some 
of which will be cited below, proved the feasibility of this method, at 
(898) 
