On the Vents of Hot Vapor in Tuscany. 203 
erack more or less vertical, and which presents no impediment, 
the muddy liquid rapidly attains its maximum heat, which is so 
intense, that, as M. Lardarel, Jun. informed me, no instrument 
had yet been made to measure accurately the maximum heat be- 
neath the surface.* It is probable that no active volcano exhibits 
greater heat at any point where a test can be applied. wenty- 
four hours of this process suffice to saturate the bubbling mixture 
with boracic acid, and the stuff is then run off into flat cisterns 
at a lower level. The fluid is there reduced to a third of its vol- 
ume by evaporation, hastened by the hot vapor being conveyed 
in tubes beneath the salt-pans, and thus saving the former cost of 
a great consumption of fuel. After the addition of soda, the desic- 
cation proceeds, and crystals of boracic acid are formed. The 
violence with which the hot gas issues from any crack, provided 
it be vertical, is such, that if stones of some weight are thrown 
upon a narrow gush of it, they are heaved up several feet into 
the air, and heavy flagstones are required to repress the eruptive 
agent, and conduct a current of it down to the drying houses 
and pans. 
man, with their natural appearance upwards of eighty years ago, 
when examined and described by Targioni Tozzetti. The thick 
with boiling muddy water, discharging gas; for the manufacturer 
now utilizes all the hot gas, and by the addition of water makes 
Oss ees dh 2 peed ct oe hi I 
* Targioni Tozzetti, the old writer, does not pretend to have ascertained the ex- 
treme heat of the vapor; but Professor Pilla, on what authority I know not, places 
it at 140° Reaumur, 
+ In rainy weather, or when change is coming on, the vapors cling to the earth 
with increased subterranean noise, and in settled fine weather they rise to a great 
