=_Chemistry_= is a science which investigates _the composition and
properties of material substances_.
Nature is composed of elementary elements; knowledge of these bodies,
of their mutual combinations, of the forces by which these combinations
are brought about, and the laws in accordance with which these forces
act, constitute chemistry, and the chemistry of steam engineering
largely deals with the foreign bodies contained in the feed water of
steam boilers.
=_Element._= In general, the word element is applied to any substance
which has as yet never been decomposed into constituents or transmuted
to any other substance, and which differs in some essential property
from every other known body. The term simple or _undecomposed
substance_ is often used synonymously with element.
There are about 70 _simple elements_, three-quarters of which are to
be met with only in minute quantities and are called rare elements.
Copper, silver, gold, iron, and sulphur are simple elements—_the metal
irridium, for example, is a rare element_—it is the metal which tips
the ends of gold pens—it is heavier than gold and much more valuable.
Probably there are not two tons of it in existence.
=_A Re-agent_= is a chemical used to investigate the qualities of some
other chemical—example, hydrochloric acid is a re-agent in finding
carbonic acid in limestone, or carbonate of lime, which when treated by
it will give up its free carbonic acid gas, which is the same as the
gas in soda water.
=_An Oxide_= is any element, such as iron, aluminium, lime, magnesia,
etc., combined with oxygen. To be an oxide _it must pass through the
state of oxidization_. Iron after it is rusted is the oxide of iron,
etc.
=_A Carbonate_= is an element, such as iron, sodium, etc., which forms
a union with carbonic acid—the latter is a mixture of carbon and
oxygen in the proportion of 1 part of carbon to 2 of oxygen. Carbonic
acid, as is well known, does not support combustion and is one of the
gases which come from perfect combustion. This acid, or what may be
better termed a gas, is plentifully distributed by nature and is found
principally combined with lime and magnesia, and in this state (_i.e._,
carbonate of lime and carbonate of magnesia) is one of the worst
enemies to a boiler.
=_An Acid_= is a liquid which contains both hydrogen and oxygen
combined with some simple element such as chlorine, sulphur, etc. It
will always turn blue litmus red, and has that peculiar taste known as
acidity; acids range in their power from the corrosive oil of vitriol
to the pleasant picric acid which gives its flavor to fruits.
=_Alkalies_= are the opposite to an acid; they are principally potash,
soda and ammonia—these combined with carbonic acid form carbonates.
Sal-soda is carbonate of soda.
=_A Chloride_= is an element combined with hydro chloric acid—common
salt is a good example of a chloride—being sodium united with the
element chlorine, which is the basis of hydro chloric acid. Chlorides
are not abundant in nature but all waters contain traces of them more
or less and they are not particularly dangerous to a boiler.
=_Sulphates_= are formed by the action of sulphuric acid (commercially
known as the oil of vitriol) upon an element, such as sodium, magnesia,
etc. The union of sodium and sulphuric acid is the well-known Glauber
salts—this is nothing more than sulphate of soda; _sulphate of lime is
nothing more than gypsum_. Sulphates are dangerous to boilers, if in
large quantities _should they give up their free acid_—the action of
the latter being to corrode the metal.
=_Silica_= is the gritty part of sand—it is also the basis of all
fibrous vegetable matter—a familiar example of this is _the ash_ which
shows in packing, which has been burnt by the heat in steam; by a
peculiar chemical treatment silica has been made into soluble glass—a
liquid. 65 per cent. of the earth’s crust is composed of silica—it
is the principal part of rock—pure white sand is silica itself—it is
composed of an element called _silicum_ combined with the oxygen of the
air. Owing to its abundance in nature and its peculiar solubility it is
found largely in all waters that come from the earth and is present in
all boiler scale.
In water analysis the term _insoluble matter_, is silica. This is one
of the least dangerous of all the impurities that are in feed water.
=_Magnesia_= is a fine, light, white powder, having neither taste nor
smell, almost insoluble in boiling, but less so in cold water. Magnesia
as found in feed water exists in two states, oxide and a carbonate,
when in the latter form and free from the traces of iron, tends to give
the yellow coloring matter to scale—in R. R. work, yellow scale is
called magnesia scale.
=_Carbonate of Magnesia_= is somewhat more soluble in cold than in hot
water, but still requires to dissolve it 9,000 parts of the latter and
2,493 of former.
Magnesia, in combination with silica, enters largely into the
composition of many rocks and minerals, such as soapstone, asbestos,
etc.
=_Lime_=, whose chemical name is _calcium_, is a white alkaline earthy
powder obtained from the native carbonates of lime, such as the
different calcerous stones and sea shells, by driving off the carbonic
acid in the process of calcination or burning.
Lime is procured on a large scale by burning the stone in furnaces
called kilns, either mixed with the fuel or exposed to the heated air
and flames that proceed from side fires through the central cavity of
the furnace in which the stones are collected.
The calcined stones may retain their original form or crumble in part
to powder; if protected from air and moisture they can afterwards be
preserved without change.
=_Soda_= is a grayish white solid, fusing at a red heat, volatile with
difficulty, and having an intense affinity for water, with which it
combines with great evolution of heat.
The only reagent which is available for distinguishing its salts from
those of the other alkalies is a solution of antimoniate of potash,
which gives a white precipitate even in diluted solutions.
=_Sodium_= _is the metallic base of soda._ It is silver white with
a high lustre; crystallizes in cubes; of the consistence of wax at
ordinary temperatures, and completely liquid at 194°, and volatilizes
at a bright red heat. It is very generally diffused throughout nature
though apparently somewhat less abundantly than potassium in the solid
crust of the globe.
=_Salt_=, the chloride of sodium, a natural compound of one atom of
chloride and one of sodium. It occurs as a rock inter-stratified with
marl, and sandstones, and gypsum, and as an element of salt springs,
sea water, and salt water lakes.
The proportions of its elements are 60.4 per cent. of chlorine and 39.6
per cent. of sodium.
In salt made of sea water the salts of magnesia with a little sulphate
of lime are the principal impurities.
The above mentioned chemical substances can be classified into two
distinct classes, _i.e._, incrusting and non-incrusting.
Of the incrusting salts, carbonate of magnesia is the most
objectionable, and any feed water that contains a dozen grains per
gallon of magnesia can be expected to have a most injurious effect on
the boiler, causing corrosion and pitting. Carbonate of lime, while not
as bad as the magnesia carbonate, yet has a very destructive action on
a boiler and 20 grains per gallon of this is considered bad water. All
silicates, oxides of iron, and aluminium, and sulphate of lime are also
incrusting. The non-incrusting substances are three, viz., chloride of
sodium (common salt), and sulphate and carbonate of soda.