The tube is
connected with a pump working at a gentle pressure, and the solution is
filtered through the tube with the aid of a small funnel (fig. 77). The
residue is washed, first with dilute hydrochloric acid, and then with
distilled water. The tube is dried by aspirating air through it, and
gently warming with a Bunsen burner. The tube is then placed in a small
combustion-furnace, and connected with calcium chloride and potash
bulbs, as shown in fig. 78. The potash bulb to the right of the figure
must be weighed. A slow stream of air is drawn through the apparatus,
and the heat gradually raised; in from thirty minutes to one hour the
combustion will be complete. The potash bulbs are then disconnected and
weighed, and the increase multiplied by 0.2727 gives the weight of
carbon.
CARBONATES.
Carbon dioxide, which is formed by the complete oxidation of carbon, is
a gas with a sweetish odour and taste, having a strong affinity for
alkalies, and forming a series of compounds termed carbonates. The gas
itself occurs in nature, and is sometimes met with in quantity in
mining. The carbonates occur largely in nature, forming mountain masses
of limestone, &c. Carbonates of many of the metals, such as carbonate of
lead (cerussite), carbonate of iron (chalybite), carbonates of copper
(malachite and chessylite), and carbonate of magnesia (magnesite), are
common.
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