Chemistry and Physics, 485 
apparatus is sacar and again weighed, but as before, only to 
decigrams. The apparatus is now immersed in the vapor of boiling 
sulphur, which, according to the oe et of Regnault has a 
constant t temperature of 442°2° when the barometer stands at. 
723°5 m The substance passes into visio? and a considerable 
— of the alloy overflows and the tension of the vapor thus 
formed is evidently measured by the height of the barometer 
column at the time, plus the equivalent in mercury of the height 
of the column of melted metal which fills the neck of the apparatus 
above the level of the metal in the bulb. The last is easily meas- 
ured with a millimeter scale if at the instant of peed the apparatus 
from the sulphur bath the levél of the metal is arked on the bulb, 
which may be easily done with melted seers wax, using a heated 
glass rod as a pen. hen now the apparatus has partially cooled 
and the adhering particles of metal have been removed, it is 
weighed for the third time and from the three weights we easily> 
ascertain what quantity of metal has overflowed in the sulphur 
wb ¢c. ¢., so that its density was about two-thirds of that of 
mercu From these values he deduces the following formula 
for the eeletacion of the vapor _— from such observations as 
we have described : 
Density (referred to air as unity) = Woaets WHET 3h)? 
* This is the pr hap of the barometer at Zurich where Meyer’s Persea 
tions were made. e mean level of the sea with the mean height 760 mm. 
the boiling point is eatin nearly 
At the sea level when the barometer stands at 760 mm. this constant 
du ced. 
2 
the tension in millime by H’. The density of the vapor is equal to its ee 
divided by the et er the same volume of air at the same temperature 
sion, or d = — and as is well known, 
ra : 
ohis 1 a ig 
w’ = 0':001293 (71 5-9-003665-444~2) ~ 760° 
But in the process we are consiflering the volume of the vapor is evidently equal 
to the volume of the overflow at 444°2° less that of the overflow which bose : 
; “10 
(Ww —0-036 W’) and as we have seen, H’ = H+ $h. Making now the substitu- 
tions and combining the numerical wala we obtain the expression given above. 
