f Chemistry. xl 
questions remain still unresolved. The view which Mr. Dalton 
has taken of the thermometer and of expansion in the first volume 
of his System of Chemistry, has drawn the attention of philoso- 
phers to the subject, and seems to have led the pha: of 
Sciences of Paris to make it the subject of a prize, which was 
pained by MM. Dulong and Petit. A translation of their paper 
as appeared in our 13th volume. The experiments which it 
contains seem to have been made with much care; and are, 
therefore, calculated to decide our opinion respecting this very 
important but intricate subject. I shall endeavour to lay the 
facts which these gentlemen have established before my readers. 
A preliminary point of some importance was the temperature 
at which mercury boils ; or, in other words, what is the bulk of 
mercury when heated to the boiling temperature compared with 
its bulk at the temperature of 32°. Their mode of determining 
this point was exceedingly ingenious, and appears quite satisfac- 
tory. They filled a glass tube, shut at one end, and drawn out 
mto a capillary point at the other, with mercury at the tempera- 
ture of 32°. The tube thus filled was weighed, and the quantity 
of mercury which it contained determined. The tube was then 
kept in boiling mercury till it had acquired the temperature of 
that liquid; while the pressure ered by the mercury in the 
capillary part of the tube prevented the mercury in the tube from 
boiling or any vapour from being formed. When the mercury 
was boiling hot, the capillary point of the tube was apcipsticnly 
sealed by the blow-pipe, and the whole tube was allowed to cool. 
It was then weighed, and the weight of the mercury which it 
contained was ascertained. The comparison of this weight with 
that of the mercury at 32° gave the expansion of mercury at its 
boiling point; and knowing how much mercury expands between 
32° and 212° it was easy to determine at what degree the mercury 
in a thermometer would stand if the whole of it were raised to 
the boiling temperature, and if the dilatation of the glass were 
abstracted. The result of the experiment made in this way is, 
that mercury boils when raised to the temperature of 360° cen- 
tigrade, which is equivalent to 680° Fahr. 
Another point of considerable importance, and without which 
indeed the boiling point of mercury could not be determined with 
precision, was to ascertain the absolute expansion of this liquid 
at different temperatures. The mode employed, though not 
altogether new, was, however exceedingly ingenious, and seems 
to have answered the purpose perfectly. It was founded upon 
the well-known hydrostatical fact, that if two liquids be poured 
into the opposite legs of an inverted syphon, the height of each 
will be inversely as its density. They filled an inverted syphon 
with mercury. One leg was kept at 32°, by being surrounded 
with a mixture of snow and water; while the mercury in the 
other leg was raised to different temperatures, by being sur- 
rounded with hot oil. The difference between, the height of the 
