Chlorine gas, which is obtained from the chloride of sodium, was discovered by Scheele in 1777, who named it dephlogisticated muriatic acid. Berthollet in 1785 termed it oxygenated muriatic acid. Sir Humphry Davy called it chlorine (from χλωρὸς, green) on account of its colour, and it has kept this name ever since. We thus see that salt is of great use to the chemist, for he not only obtains chlorine gas from it, but also hydrochloric acid, a most useful and efficacious drug in the treatment of some hepatic diseases. Chlorine also enters into combination with other chemical substances known as chlorides and chlorates, sub-chlorides and per-chlorides; for instance, we have the chloride of ammonium and the chlorate of potash; we also have the sub-chloride of mercury, or calomel, and the perchloride of mercury, or corrosive sublimate, with various others.
According to Pereira, hydrochloric acid was known to Djafar, or Geber, an Arabian chemist who flourished in the eighth century, and whom Roger Bacon calls magister magistrorum. Everyone is acquainted with the chloride of lime, a substance so generally used for household and disinfecting purposes, that I need only mention it; besides this, there are other salts with which chlorine enters into combination.
Formerly, to bleach cotton it was required to expose the material to the action of the sun and air, rendering the process long and tedious, as it took on the average quite six or eight months, and likewise a large surface of land was necessary for the operation.
Now, owing to chlorine gas, the process is completed in a few hours, and a comparatively small building is quite sufficient for the purpose; the fibre is beautifully and permanently whitened, and the manufacturer experiences the pleasing satisfaction of a more rapid remuneration.
Where would be our delicately white textile fibres were it not for the abundant and inexhaustible supply of salt? How should we be enabled to cause vegetable colours to vanish as if touched by the hand of a magician were it not for the bleaching properties of chlorine? And how should we be able to procure this green-coloured gas which produces these changes were it not for the chloride of sodium?
As a therapeutical agent chlorine possesses some characteristics peculiar to itself: it is used as a lotion for cancerous growths and foul ulcers, also for some cutaneous eruptions. It is likewise used as a vapour-bath; it has also been used in the treatment of chronic bronchitis and phthisis, and as a gargle in certain morbid conditions of the mouth. When chlorine is absorbed by the system it is supposed to possess some antiseptic and alterative action, acting specifically on the liver.
There is one more fact of a chemical nature in reference to chlorine which it would be unwise to throw aside, as it possesses some degree of interest. When the chemist wishes to decompose water, or in other words to liberate hydrogen from oxygen, he has no better agent to effect the purpose than this greenish-coloured gas, because it has such a strong affinity for hydrogen, which is one of the most characteristic properties of chlorine. Mix them together, and they combine with explosive violence if they are exposed to the beams of the sun. By this process we obtain hydrochloric acid gas, while the oxygen is liberated.
Chlorine only becomes active when it is associated with moisture; when dry it is quite inert as regards its bleaching powers, for “when moist it gradually decomposes the water, combining with its hydrogen, and disengaging its oxygen; and it is this oxygen, at the moment of its liberation, which is the really active agent in bleaching.”[28]
Salt, like other inorganic compounds, has been known to act as a poison when taken in a large quantity, and Dr. Alfred Taylor, the eminent toxicologist, mentions a case in which a table-spoonful was taken by mistake for sugar; there was no vomiting or purging, but great pain in the region of the stomach, with dryness of the fauces, which lasted several days. Did not the above emanate from so great an authority, one would feel inclined to question it. Could anyone take such a large amount and swallow the same without being immediately aware of his mistake? Surely he would have immediately and spasmodically ejected it by reason of its extremely pungent character, before it had even reached the fauces.
Dr. Taylor says that “in a toxicological view it is not easy to distinguish the effects of common salt in these cases from the poisonous action of salt of sorrel, or binoxalate of potash, which it is well known may be taken with impunity in small quantity;” the symptoms are those of irritant poisoning, causing great pain and intensely inflaming the stomach and intestines, and in those few cases which we have on record the vomiting was excessive.