CARBONATES. 
been found that, by charring the inside of casks 
for keeping water, it may be preserved a long 
time without spoiling. Charcoal can even re- 
move or prevent the putrescence of animal mat- 
ter. If a piece of flesh has become tainted, the 
taste and smell may, in a:great measure, be re- 
moved, by rubbing it with charcoal powder; and 
it may be preserved fresh for some time by bury- 
ing it in the same substance. To produce these 
effects, however, it is necessary that the charcoal 
should have been well calcined and newly pre- 
pared.—The uses of charcoal are extensive. It is 
used as fuel in various arts, where a strong heat 
is required without smoke, as in dyeing, and in 
various metallurgic operations. By cementation 
with charcoal, iron is converted into steel. It is 
used in the manufacture of gunpowder, in its 
finer state of aggregation, under the form of 
ivory-black, lamp-black, &c. It is the basis of 
| black paint; and, mixed with fat oils and resin- 
ous matter, to give a due consistence, it forms 
the composition of printing ink. It is used to 
destroy colour and odour, particularly in syrups ; 
to purify honey ; to resist putrefaction; to con- 
fine heat, and for a number of other important 
purposes.— When charcoal is heated to a certain 
degree in the open air, or in oxygen gas, it takes 
fire, and burns with the production of an elastic 
vapour, which has been called Carsonic Acip 
Gas. See that article. 
CARBONATES. Salts consisting of carbonic 
acid in combination with alkaline or metallic 
bases. They are attacked and decomposed by 
nearly all other acids than their own; and while 
| undergoing decomposition, or sending off their 
carbonic acid into the atmosphere, and surren- 
dering their bases to the attacking acids, they 
exhibit the beautiful phenomenon of efferves- 
cence. The carbonates of lime and magnesia are 
deprived of their carbonic acid, and reduced to 
a caustic, or, in old chemical language, a cal- 
cined state, by the application of a full red heat ; 
the carbonates of baryta and strontia are decom- 
posed by an intense white heat; the carbonates 
of soda, potash, and lithia, cannot be decomposed 
by mere heat ; and all the other carbonates are 
deprived of their carbonic acid by a dull red 
heat. All the carbonates are more or less affected 
by an excess of carbonic acid, so as to imbibe 
more of it and form supercarbonates; and all, 
excepting those of soda, potash, and ammonia, 
are very sparingly soluble in pure water, The 
carbonates of lime, magnesia, strontia, baryta, 
soda, and manganese, and the double carbonate 
of lime and magnesia, are found naturally exist- 
ing; but most of the others are formed by arti- 
ficial processes, or with some artificial aids. 
Some of the carbonates, particularly those of 
lime, magnesia, soda, potash, iron, and manga- 
nese, play a very prominent part as constituents 
of soil, either natural or added ; but they will be 
noticed, as to their individual nature and their 
| respective modes of action, in the articles Lims, 
693 
CARBONIC ACID. 
Maenesta, Sopa, Porasu, Iron, and Maneanese. 
The carbonate of ammonia contained in rain 
water also performs most important functions in 
the feeding of vegetables, and consequently in 
the chemical processes of afarm. See the article 
Ammonra. Several of the carbonates—especially 
those of lime, soda, potash, and magnesia—be- 
sides acting directly, as constituents of soil, upon 
plants or upon their food, perform the great of- 
fices, jointly with the carbonic acid of the atmo- 
sphere, of attacking and reducing the silicates, 
which, but for their action, would form an ingre- 
dient of soil as stationary and unyielding as it is 
widely diffused and bulky. “ The silicic acid,” 
remarks Dr. Dana, “ acts on the lime, forming 
silicate of lime; while the carbonic acid, now let 
loose, acts as such upon other silicates, and eli- 
minates or frees the alkaline bases. Let it be 
supposed that there is silicate of alumina, that is 
clay, or silicate of potash and alumina, in the 
soil. Let carbonate of lime, that is marble, and 
slacked lime, shells, &c., be added to the soil. 
The result is that, slowly but surely, chemical 
action takes place, the silicic acid pulling one 
way, and the carbonic acid another, the lime is 
changed to silicate of lime, and the carbonic acid 
escapes, and now in its turn acts upon silicates 
as did carbonic acid of air. The alumina remains, 
the soil becomes more clayey. Thus sands by 
liming are amended. This principle of the action 
of carbonates, unravels the mysterious action of 
a vast variety of substances, which appear to be 
very ineit and inefficient. It must be remem- 
bered, that the action of silicates and salts is 
alone under consideration, uninfluenced by the 
presence of geine or plants. That action in its 
simplest form constitutes the following, which 
may be laid down as the ninth principle of agri- 
cultural chemistry,—carbonic acid and the car- 
bonates decompose the earthy, alkaline, and me- 
tallic silicates of soil.” — Turner's Elements of 
Chenistry.—Lrebig’s Chemistry of Agriculture— 
Johnson's Lectures on Agricultural Chemistry.— 
Dr. Danws Muck Manual—Chaptal’s Chemistry 
applied to Agriculture. 
CARBONIC ACID. A colourless, inodorous, 
elastic fluid, consisting of one equivalent of 
carbon and two equivalents of oxygen. It 
possesses, In an eminent degree, all the physical 
properties of the gases, and cannot be con- 
densed into a liquid under a less pressure than 
one of thirty-six atmospheres. It consists, 
by volume, of equal volumes of carbon vapour 
and oxygen gas; and, by weight, of six parts of 
carbon and sixteen of oxygen. Its specific gra- 
vity is estimated by Dulong and Berzelius at 
1524, and by Dr. Thomson at 15277; so that, 
according to the latter estimate, 100 cubic inches 
of it weigh 47'377 grains. 
Carbonic acid was discovered, in 1757, by Dr. 
Black; and was, for a considerable time after- 
wards, known under the name of fixed air. Its 
composition was first demonstrated synthetically 
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