470 Natural-Philosophical Collections. 
that the upper galleries allow it to escape in abundance, although their communi- 
cation with below is intercepted. by the lower gallery. The disengagement in 
the upper parts of the vein is of short duration, whereas a continual and very vio- 
lent ebullition manifests itself in the waters which run upon the floor of the 
lower gallery. 
Sometimes the disengagement of the gas is intermittent with very near periods. 
Thus, in the first upper gallery, about a fathom beyond the branching of the 
vein, a fissure was met with, which roared loudly during a quarter of an hour, 
ceased to be heard during the same time, and recommenced in the same manner. 
After some days the phenomenon disappeared. : 
When intermittence takes place, it is sufficient to sound the fissure with a 
stick, to make the rumbling recommence. At the floor of the gallery there oc- 
curs a similar spring, whose intermissions are at shorter periods. It is remark- 
able that the gas is more abundant in the galleries during westerly winds and in 
stormy weather; and then the quantity sometimes becomes so great, that it is 
impossible to remain in the lower works, whereas, in ordinary cases, the gas does 
not rise more than a few inches above the ground. ‘The temperature increases 
considerably in the parts filled with gas, which assimilates this phenomenon to 
that of hot springs. 
M. Fournet remarks, that the phenomenon which is observed at Pontgiband 
had been considered as unique in the Annales des Mines, and yet that several 
cases of a like nature have already been met with. For example, Alonzo Barba, 
a Spanish metallurgist, mentioned in 1630 a disengagement of gas which had 
““ a smell similar to that which one breathes in a cellar filled with new wine, in a 
state of fermentation.” 
Carbonic acid gas occurs, in many places, in the neighbourhood of Pontgi- 
baud. When it is dissolved in water, it acts as a solvent upon certain mineral 
substances, and especially the carbonates of lime, iron, and manganese. 
M. Fournet imagined, at first, that it came from the volcanic agents which 
have overturned Auvergne, a conclusion countenanced by the circumstances of 
other deposits of similar formation presenting the same springs. But it must be 
observed that, in some countries, as Corsica, Auvergne, and the Vosges, gaseous 
springs are also met with in limestone formations.—Annales Scientifiques, litter. 
et indusir. de V Auvergne, June 1829. 
Chemistry.—M. Despretz communicated to the Academy of Sciences, on the 
(18th January last, the following results, derived from his chemical researches. 
1. Nickel, cobalt, zinc, and tin, at a red heat, possess, like iron, the property 
of decomposing water ; and their oxides, at the same temperature, are reduced by 
hydrogen gas. 
2. Carbonic acid is acted upon in the same way as water: it is transformed by 
zinc and tin into oxide of carbon, and this latter gas completely reduces the oxides 
of the three metals. Herein we see a fact, which has been considered to be ano- 
malous, extended to many metals, and to many binary bodies. 
3. Crystallizable acetic acid may be prepared by heating a mixture of acetate 
of lead, and of a proportional of concentrated sulphuric acid. The process by 
which the acid is obtained is kept secret by the discoverer, who supplies all the 
laboratories in Paris. 
4, By placing in a good furnace, at a high temperature, a mixture of sulphur 
and of oxide of zinc, a sulphuret of zinc is produced, which experienced minera- 
logists have confounded with blende, (native sulphuret of zinc.) 
Sulphate and Carbonate of Magnesia from Magnesian Limesione.—M. Pel- 
letier has announced to the Academy of Sciences the discovery of a process, by 
which he has obtained the sulphate and carbonate of magnesia in great quantities 
from the magnesian limestone, of which there exist in France many beds, hitherto 
unknown. 
