498 M. F. Braun on the 
Hg(Na+K)* . ¢=20°; T=380°. 
PbSn:. . (J...) 20°; T=435°; t=424° ie 
IemST 92) 5 1=508°; T = 882°. 
He(Hg + Bi+ Pb)tt=20°; P= 5305. 
A, For the determination of high temperatures in spaces 
frequently small I employed spirals of platinum wire, whose 
galvanic resistance had previously been determined as a func- 
tion of the temperature. I employed for this purpose a large 
muffle furnace heated by coal, the description of which, as 
well as of other experiments made with it, I propose to give 
shortly elsewhere. The vessels for the air-thermometer were 
made of Meissen porcelain {. The dimensions could be so 
chosen that, assuming constancy of temperature, temperatures 
of 1000° C. could be accurately measured to 1° or 2°. 
5. The metals were enclosed in glass tubes, wherever glass 
could be used. Platinum wires melted into the glass served 
for external connections. With some metals the platinum 
wire was in direct contact with the metals ; with others this 
contact was made by means of a pencil of retort-carbon § or 
graphite, with others by means of an iron-wire. Two glass 
tubes filled with metal were placed vertically side by side. 
At the hotter (upper) point of junction the platinum wires 
were melted together outside the tubes by means of the oxy- 
hydrogen blowpipe. So far as the wires which serve to make 
contact with the fluid metal at the hottest and coolest points 
penetrate the ends of the tubes, uniformity of temperature 
must be maintained. The cooler (lower) ends of the tubes 
were plunged into two concentric vessels full of mercury, which 
were placed in a bath of constant temperature, though not 
always the temperature of the room. From these mercur 
vessels wires of lead conducted to a petroleum bath of the 
temperature of the room, from which the copper connections 
were made. ‘The leaden wires of course could not be placed 
directly in contact with the mercury. Their ends were 
melted intoa glass tube, through the lower closed end of 
which a short platinum wire passed. I pass over here 
the precautions found necessary in order to ensure that the 
* Alloy liquid at ordinary temperatures; about 1 eq. K to 1 eq. Na. 
+ Alloy liquid at ordinary temperatures; 1 part lead, 1 part bismuth, 
3 parts mercury. 
{ I wish here to express my obligations to the Royal Saxon Porcelain 
Manufactory, and especially to M. Bittner, for the great trouble which 
they have taken in the very difficult manufacture of these vessels. 
§ Platinum at 200° is amalgamated by mercury, and at about 500° 
is dissolved as energetically by mercury as it would be by boiling aqua 
regia. 
