SEPTEMBER 3, 1897. ] 
the air thermometer standard of that insti- 
tution. Data have also been supplied by 
Callendar. Among these values there is as 
yet considerable confusion and the end is 
not yet. Long ago I suspected that the 
Violle melting points were probably too low, 
whereas the assumed zine boiling point is 
probably too high. This surmise has been 
partially borne out by the Reichsanstalt, 
though Le Chatelier even now prefers 
Violle’s values. * 
Thermoscopes based on a specific heat have 
an advantage over fusion thermoscopes in 
pot being discontinuous. They are quite 
as ‘intrinsic’ and much less convenient in 
practice. Guyton-Morveau, at the begin- 
ning of the century, pointed out the pyrome- 
ter importance of specific heat, and a host 
of observers followed him. But the critical 
discussion of the subject is due to Pouillet 
(1836), who determined the thermal capac- 
ity of platinum between 0 and 1200° abso- 
lutely, and found a value so nearly constant 
as to place this method of pyrometry in a 
very favorable light. Other observers fol- 
lowed with new data, and the bulk of our 
knowledge to-day is again due to Violle. 
Violle used Deville and Troost’s exhaustion 
air thermometer and determined the law of 
variations of specific heat and temperature 
throughout a large pyrometric interval, with 
a number of metals, silver, gold, copper, 
palladium, platinum, iridium, among them. 
It was by prolonging this law as far as 
fusion that the melting points of the metals, 
to which I have already alluded, were ob- 
tained. This verges on extrapolation, but 
it is not extrapolation gone mad. 
The importance of calometric high tem- 
perature measurement has recently been 
accentuated in connection with the remark- 
* The following table contains a brief summary : 
Ag. (Violle) 954° (Barus) 986°- 985° (Callendar) 982° (H.&W.)9719 
Au, 1045° 10919-10939 10879 10729 
Cu. 10549 10969-10979 19829 
Ni. = 14769-15179 14849 
Pd. 1500° 15859-16439 15879 
Pt. 175° 17579-18559 17809 
SCIENCE. 
3939 
able high temperature accomplishments of 
Moissan. Furnace temperatures in the 
case of such technological operations as are 
used in connection with iron, glass and 
porcelain manufacture rarely exceed 1,400°, 
except perhaps in the Bessemer process, 
where the temperatures are wont to exceed 
1,600° and even reach 2,000°. In Moissan’s 
furnace, which is essentially an electric arc 
enclosed by non-conducting lime, a totally 
new order of high temperatures is impressed. 
There was thus a call for at least an 
approximate measurement of their values, 
which was answered by Violle, assuming 
that the specific heat of carbon above 
1,000° approaches a limit. The sufficiency 
of this hypothesis is not unchallenged, 
however; for instance, Le Chatelier finds 
that, up to 1,000°, the specific heat of 
carbon continually increases, having no 
certain limit. Admitting Violle’s results, 
Moissan’s furnace temperatures exceed 
2,000° even at 30 amperes 55 volts; at 
360 amperes and 70 volts tin and zinc 
oxides melt and boil; they exceed 3,000° at 
500 amperes and 70 volts, where lime melts, 
and often boils. Moissan, however, went 
as far as 1,000 amperes at 50 volts. 
The striking novelty of Moissan’s work 
is rather of chemical interest, and a large 
part of it is so fresh in our memory that, in 
view of Moissan’s forthcoming book,* I 
need merely glance at it. A range of fusi- 
bilities, among which platinum lies lowest, 
while chromium, molybdenum, uranium, 
tungsten, vanadium, follow in order, and 
of ebullitions beginning with silica and 
zinc oxide, is rather breath-taking. Finally, 
his structural investigations on the occur- 
rence of carbon, and his long series of car- 
bides, many of them commercially valuable, 
have staggered even the sensational press. 
Leaving other intrinsic thermoscopes for 
the moment, I will ask your attention in 
*Le four électrique, par Henri Moissan ; Paris, 
Steinheil. 
