258 MEASUREMENT OF HIGH TEMPERATURES. [bull. 54 
is perhaps futile. It is impossible to guaranty that in such tubes th< 
radius is either rigorously uniform throughout the length of the tub 
or that the capillary canal is truly circular in section. Coiling of tubes 
so essential in very high temperature work, also flattens the section 
In drawing tubes flaws or splinters of metal partially projecting inp 
the capillary canal can not always be obviated. But all these effect 
are not hurtful where relative results are alone of interest. This is, oi 
course, the case in pyrometry. 
Hydrogen and air, as used in the following tables, are not intender 
to refer to absolutely pure gases. Both gases were dried, of course, ii 
the usual way. But the hydrogen may contain traces of air or sul 
phide, and the air was not freed from carbonic acid. My object in th< 
following experiments was to test the possibility of an identity of lai 
in the case of two thoroughly different gases, the zero properties of eacl 
of which were continually redetermined, i. e., before each experiment i 
Inasmuch as these gases are to be true gases, all vaporous constituent 
were to be excluded. At high temperatures, however, even this pre* 
caution is not essential. 
Data. — Tables 81 and 82 contain the results of consecutive series o 
experiments made with air and with hydrogen, respectively. In thesr^ 
early experiments I did not venture to solder the terminals of the helh 
into the walls of the pneumatic trough from fear of injury to the tubes 
Hence the trough leaked at high temperatures, and the water wetting 
the outside of the asbestus chimney or furnace which surrounds thu 
helix and burner was the cause of an irregular distribution of temi 
perature, which I did not foresee. Temperature being measured in thu 
inside of the helix at a point nearest the trough is therefore 
decidedly low, for it is here that the effect of cooling the en 
vironment is seriously felt. The position of the thermo 
couple (No. 37, calibrated above) is nearly that given ii 
Fig. 47. Moreover, the helix itself is naked, that is, no 
jacketed by an envelope of mica or other substance of lov 
thermal conductivity. Temperatures near 1,000° are ob 
tained by direct exposure to the -flame of the chimneyed 
Bunsen burner: higher temperatures (usually above 1,200° 
by exposure to the flame of the air-blast lamp. Tempera I 
fig. 47. Vertical tures below 800° (usually) are obtained in the air batl'i 
section through f t h e petroleum Argand burner, the chimuey of whicl 
. helix. Scale i. . ., f, . , . , & ' J 
is suitably jacketed. 
(912) 
