Thus, Cyanide of Potassium is a true salt, although highly poisonous; Nitrate of Silver is a salt; the green Sulphate of Iron is a salt; so also is Chalk or Carbonate of Lime, which has neither taste, colour, nor smell.
On the "Hydracid" class of Salts.—The distinction between Oxyacids and Hydracids has already been pointed out ([p. 309]), the latter having been shown to consist of Hydrogen united with elements analogous in their reactions to Chlorine, Iodine, Bromine, etc.
In a salt formed by an Oxygen Acid, both the basic and acid elements appear. Thus the common Nitre, which is a Nitrate of Potash, is found by analysis to contain Oxide of Potassium as a base, in a state of combination with Nitric Acid. But if a salt be formed by neutralizing an alkali with a Hydrogen Acid, the product in that case does not contain all the elements. This is seen from the following example:—
| Hydrochloric Acid | + | Soda | |
| = | Chloride of Sodium | + | Water; |
or, stated more at length,—
| (Chlorine Hydrogen) | + | (Oxygen Sodium) | |
| = | (Chlorine Sodium) | + | (Oxygen Hydrogen). |
Observe that the Hydrogen and Oxygen, being present in the correct proportions, unite to form Water, which is an Oxide of Hydrogen. This water passes off when the solution is evaporated, and leaves the dry crystals of salt. On the other hand, with the Oxyacid Salts, the elementary Hydrogen being absent, no water is formed, and the Oxygen remains.
It must therefore be borne in mind that salts like the Chlorides, Bromides, Iodides, etc. contain only two elements; but that in the Oxyacid Salts, such as Sulphates, Nitrates, Acetates, three are present. Thus, Nitrate of Silver consists of Nitrogen, Oxygen, and Silver, but Chloride of Silver contains simply Chlorine and metallic Silver united, without Oxygen.
The Hydracid salts however, when decomposed, yield products similar to the Oxyacid salts. For instance, if Iodide of Potassium be dissolved in water, and dilute Sulphuric Acid added, this acid, being powerful in its chemical affinities, tends to appropriate to itself the alkali; but it does not remove Potassium and liberate Iodine, but takes the Oxide of Potassium and sets free Hydriodic Acid, In other words, as an atom of water is produced during the formation of a Hydracid Salt, so is an atom destroyed and made to yield up its elements in the decomposition of a Hydracid Salt.