208 HOLTZMANN ON THE HEAT AND ELASTICITY 
vapours, and the temperature ¢ is reckoned from the boiling-point 
of the fluid under consideration. Higher temperatures must in 
such case be indicated according to the air thermometer. 
24, For the vapour of mercury I obtain with the results of 
the experiment of Avogadro* the formula, 
p _ 2:0089.7¢ ; 
log Do = 34840 Ermer (9.) 
in which the temperatures are reckoned from 350°, and p, repre- 
sents, as previously, the pressure of one atmosphere. A com- 
parison of the direct observations with the results deduced from 
this formula is contained in the following table :— 
Observed temperatures, 
| x 
saint Values of ¢. starting from freezing-point. py 
mulimetres; lasses) .|P oa ls eo ul tee EL he ee 
Calculated. Observed. Air thermom. | Merc. thermom. 
58-01 — 124-37 — 124-1 225-9 230 +0°27 
80-02 —113-92 —114°5 235°5 240 —0°58 
105°88 —103°98 — 104-95 245-05 250 —1:03 
133-62 — 95°06 — 95-4 254-6 260 —0°34 
165-22 — 86:33 — 85:9 264-1 270 +0:43 
207°59 — 76°24 — 763 2737 280 —0:06 
252-51 — 66°95 — 66:8 283-2 290 +0°15 
The coincidence is, as is seen, satisfactory. 
25. From this formula results, first, the limit of evaporation 
= — 348°, i.e. this limit is situated 2° above the freezing-point 
of water. This coincides with the observation of Faraday, who 
perceived no mercurial vapour below 0°. 
26. The expansion of the vapour of mercury amounts, if we — 
start from the volume which it has at the boiling-point of mer- — 
cury, to sae or 0°00259 of its volume for every centigrade de- 
gree. 
27. The coefficient 20089 is in the former notation (see 19), 
equal M. et In this a=374 ; —= 348; and & is found from 
the statement, that at the boiling-point the vapour is 6°9785 — 
times as dense as air of the same temperature, equal 
10333 (1+ 350 x 0003668) 
1°299 .6°9785 
We thus finally obtain 4, i.e. the specific heat of mercurial va- 
= 2602. 
* Dove, Repertorium der Physik, i. Part 53. 
