SEPTEMBER 3, 1897. | 
of Becquerel’s results, and his original re- 
search, with its applications to fusion, to 
radiation, to thermo-electrics, etc., is one 
of the noteworthy accomplishments in the 
history of pyrometry. Nevertheless, it must 
not be forgotten that to the investigation 
of Deville and Troost our knowledge of the 
perviousness of iron, platinum and other 
metals to gases is due. We are also in- 
debted to Deville for the great discovery of 
dissociation, the very phenomenon which 
he was here so loth to acknowledge. This 
is the case of a man stumbling in his own 
footprints. Victor Meyer was, I believe, 
the first to point out the probable dis- 
sociability of the iodine molecule, suggest- 
ing a fruitful subject of research which has 
since been extended to many other mole- 
cules. 
In 1863 Deville and Troost began a new 
series of high temperature researches, the 
feature of which is the perfected form of 
porcelain bulb. This was a hollow sphere 
and long capillary stem adapted for use 
with Regnault’s standard air thermometer. 
Great difficulties were encountered in the 
endeavor to glaze the bulbs within. They 
were finally overcome by making bulb and 
stem separately and then soldering them 
together with feldspar before the oxy-hy- 
drogen blow pipe. Elaborate measure- 
ments on the thermal expansion of Bayeux 
porcelain accompany these researches which, 
undertaken together with M. Gosse of the 
Bayeux works, occupied them intermit- 
tently for about seven years. A full sum- 
mary of their data did not appear, however, 
until 1880, when, together with a new 
vacuum method of high temperature air 
thermometry, they communicated the re- 
sults of twenty-seven measurements on the 
boiling point of zinc. Their new results 
are in good accord with the data of Bec- 
querel already cited and the more recent 
results of Violle and others for the same 
landmark in the region of high tempera- 
SCIENCE. 
341 
tures. Measurements between 0° and 
1500° had thus reached a degree of pre- 
cision of about 15° in 1000°. 
The further development of pyrometry 
took a somewhat different direction. Reg- 
nault (1861) had already made use of a 
displacement method, in which the meas- 
uring gas is removed bodily into the meas- 
uring apparatus by an absorbable gas. But 
the method was independently revived by 
Professor Crafts, of the Boston Institute of 
Technology. These methods are not of 
especial excellence below 1500° ; but above 
that temperature, when most solids tend to © 
become viscous, their importance increases 
(as Crafts duly pointed out) in proportion 
to the rapidity with which the measuring 
operations can be completed. One or two 
minutes may suffice and different gases 
may be tested consecutively. It is in this 
way that Victor Meyer and his pupils, 
after demonstrating the dissociation of 
iodine and chlorine molecules, succeeded in 
penetrating quantitatively to very much 
less accessible heights of temperature. A 
particular desideratum was a rigid test as 
to the stability of the molecule of the 
standard measuring gases (oxygen, hydro- 
gen, nitrogen). The results were favorable, 
inasmuch as for these and for many gases 
like CO,, SO,, HCl, Hg, etc., the expansions 
obtained were linear functions of each other. 
In their final work, temperatures as high 
as 1700° were reached, the air thermometer 
for this purpose being tubular in form, con- 
sisting of very refractory fire clay with an 
interior and exterior lining of platinum and 
with two end tubulures of platinum for in- 
flux and efflux of gases. Among many re- 
sults of great chemical interest their re- 
searches showed that metallic vapors, phos- 
phorus, sulphur, etc., at high temperatures 
tend to pass into the monatomic or the dia- 
tomic molecular structure. 
Sometime after (1887) a series of experi- 
ments furthering the line of research of 
