180 MEASUREMENT OF HIGH TEMPERATURES. [bull. 
stop-cock B is supposed to be in communication with the hydrogu 
generator 5 the stop-cocks G and D are connected by rubber tubiu \ 
the stop-cock E, finally, supplies the hydrogen to the blow-pipe, wi i 
which it is in communication. The advantage gained in this way 
this, that the hydrogen may be generated and used at the same time- 
a desideratum when large quantities of the gas are necessary. 
Revolving muffle. — In order that the temperature comparisons in que 
tion may be satisfactorily made, the apparatus to be compared must 1 
placed in a space of practically constant temperature, which shall 1 
variable at pleasure from ordinary temperatures to the. most extren 
degrees of white heat. Methods for securing constant temperatures f< 
thermo-electric comparisons have already been given; but when one t 
the pieces of apparatus to be heated is as large as the bulb of an a 
thermometer, and when, moreover, this relatively large apparatus is i 
be compared with the sensitive point of the thermo-element, the dif 
culties of calibration are very much increased. In some of the earJ 
comparisons the efficient assay muffle-furnace made by the Buffa! 
Dental Manufacturing Company was used. This is practically a g 
gautic Bunsen burner, surmounted by a furnace of fire-clay, so coi 
structed that the flame in a narrow sheet is compelled to pass aroun 
and completely to envelop the muffle. In the furnace used this mufifj 
was fully 20 cm long and 12 ,m high, offering ample space for the iutroduj 
tion of the bull), and by wrapping asbestus paper and carded asbestr 
thickly around the bulb so as quite to fill the muffle, and binding miirE 
and thermoelement closely together, the two may be compared wit 
some accuracy. Eesults of this kind are given below (p. 201.) 
Unfortunately the introduction of metal envelopes is objectionable, j 
view of the danger of fluxing the contiguous parts of refractory claj 
There are other and more serious difficulties encountered. The maxim ui 
temperature thus attainable is not greater than 1,000°, and hence the ii 
terval of calibration is limited. Moreover, the closed end of the muflj 
is at the center of heat of the furnace, whereas the open end is neitln 
surrounded by flame nor are the provisions against loss of heat sufl 
cient for constant temperature — conditions which recommend the fu| 
nace for assay purposes, but which, inasmuch as they involve diffe 
ences of temperature of several hundred degrees, are seriously obj] 
tionable for calibration purposes. Again, the rate of cooling of tn| 
furnace is too great. It is difficult to close up so completely as 
exclude convective cooling due to currents of air and diminish loi 
by radiation,- the bottom of the furnace over the burner being larj 
open, and inaccessible, and the chimney large. Nor is it convenient] 
possible to regulate the flame of the burner for intensities of heat lej 
than the maximum. Finally, thermo elements mast be compared singly 
because they need to be tied to the bulb. In general consecutive cori 
parisons of series of elements are desired. 
Without question the form of the furnace could be modified to ina 
($34) 
