FOREIGN CORRESPONDENCE. 
that of the carbonic acid gas (if we consider the maximum) as 6*4 : 93'6 
— oxygen appears to be completely absent. Nitrogen, on the con- 
trary, is always present, in the proportion of from 2 to 3 per cent. 
3, and finally, comes a fact which MSI. Ch. Deville and Leblanc 
have been the first to observe : In every case these gaseous mixtures 
contain a certain quantity of free hydrogen gas and protocarbide of 
hydr.igen (C^ H ) which both measured together attain, on an average, 
the same per-centage as the nitrogen. In some places, for instance, in 
a crack or fissure that joins Laderello and Castelnuovo, the proportion 
between these two combustible gases is nearly as 1 : 1. 
The presence of hydrogen in these gaseous emanations of Tuscany 
affords a new feature of resemblance between them and the famous 
Geysers and Solfatara of Iceland, but up to the present time we are 
not aware that any of the acute observers who have studied the Iceland 
emanations have ever remarked in them the presence of carburetted 
hydrogen. 
Closing the memoir quoted above, we will add here a few remarks 
upon boracic acid, as it is a very interesting natural production. 
Before it was discovered dissolved in the waters of the Tuscan lagoni, 
all the horax used in metallurgical operations, in medicine, and by the 
mineralogist in his essays with the blow-pipe, came from Asia — prin- 
cipally from India. Jfow, the boric acid of Tuscany is converted into 
borax (bi-borate of soda), for the arts and manufactures. The natural 
acid only contains 56 per cent, of pure acid, the remainder being 
water. 
Boric acid (or boracic acid, as it is often called), though not volatile 
when pure, even at a high temperature, possesses the peculiar property 
of being volatile in watery vapour ; so that, if a dissolution of it be 
distilled in a retort, a certain quantity of the acid will be found to have 
passed over with the steam, and will slowly deposit itself in the reci- 
pient, where it will crystallize in beautiful little white crystals. This 
is pretty nearly what takes place in nature. Besides the invisible 
vapour with which the air is constantly more or less charged, and which 
is every now and then condensed in the shape of clouds or fog, there is 
a constant supply of watery vapour, that makes its way (together 
with the gases of which we have been speaking above), through the 
fissures of certain rocks, either volcanos, solfatara, or calcareous and 
serpentine formations. These vapours are evolved from the earth near, 
at, or above boiling point (100° centigrade), with a hissing noise, and 
sometimes from high white columns of steam, that are visible from 
afar. This is the phenomenon to which the Italians have given the 
name of fumarolla, and which is nowhere more strikingly grand than 
in Tuscany, in the calcareous hills (often associated with serpentine) 
of Monte-Cerboli, Castelnuovo, and Moute-Rotondo. 
This projected vapour carries with it boric acid and the gases noticed 
above. The vapours rise either directly from clefts in the rocks or 
from stagnant pools, in which they throw up small cones of mud ; in 
places where the boric acid vapours permeate the fissures of the rocks, 
they deposit sulphur. The boric acid is dissolved by the water, which 
constantly condenses from the fumarolle, and forms the lagoni, from 
