170 MEASUREMENT OF HIGH TEMPEEATURES. [bull. 54. 
Heat must be cautiously applied to prevent the cement from running 
in far enough to stop up the capillary canals. I may add here that in 
later experiments I found it best to solder the ends of the capillary 
tubes into a little cylinder of brass, retaining in other respects the ad- 
justment of Fig. 30. The brass cylinder is, of course, provided with two 
holes to receive the tubes. I have also in definite work discarded 
stop-cocks altogether, cementing either an open glass tube or a little 
closed glass cup around the brass cylinder in question, according as I 
wished to exhaust or to dry the air in the bulb or to make thermal 
measurements. 
Capillary tubes may be made either of copper, of silver, or of plati- 
num. The latter are preferable, because they do not amalgamate, and 
if a mercury thread is accidentally forced into them, it can be forced 
out again cleanly, like the thread of a thermometer. Threads accident- 
ally injected seldom pass beyond the stop-cock L R, and thus the fatal 
accident of the injection of mercury into the thermometer bulb P is 
avoided. The capillary tubes should be seamless. I succeeded in 
making them of copper pretty well as follows: Taking a cylindrical 
copper rod l cm in diameter and in convenient lengths of 5 cm to 10 c,n , 
central holes were drilled into them about 0.4 cm to 0.6 cm in diameter, as 
nearly as possible co-axial with the rod. These holes were then filled 
with fusible metal, and when cold the rods were rolled and drawn 
down to fine wire of the diameter required. The tubes were submerged 
carefully in boiling aniline, commencing at one end and passing to the 
other; this to prevent rupture in virtue of sudden expansion of the 
fusible core. By means of an air force-pump, or even of a high-press- 
ure steam-boiler, acting at one end, sufficient pressure was brought to 
bear on the fused core to force it out completely. When this occurs 
bubbles issuing at the end of the tube rise in the aniline in great num- 
ber. The tubes are then withdrawn from the bath, dried, and, with a 
current of steam passing through them, heated to redness, and tested. 
This process is very tedious, inasmuch as it is not always possible td 
so draw the tubes that the fusible metallic core remains central. When 
the canal is asymmetric there is liability to rupture, if it does not actu- 
ally occur during the drawing. 1 For each perfect tube two or three in 
perfect ones must be discarded. Tubes thus made have a larger caliber 
relative to their thickness than is obtainable iu other ways. Thin- 
walled capillary tubes are often specially desirable, particularly when 
tubes are to be soldered (with glaze) into the stem of an air thermome- 
ter. In table 41 1 give the constants of copper tubes obtained by this 
process. 
1 According to Ronina (cf. Spring: Chem. Ber., vol. 15, 1882, p. 595) silver with M 
platinum core (Wollaston's method) is found to alloy after long drawing. I observed- 
no effects of this kind, however, possibly because the metallic surfaces, in case of 
base metals, are not sufficiently clean. 
(824) 
