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.