Читать книгу The History of Salt - Evan Martlett Boddy - Страница 6

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SALT AS A CHEMICAL, THERAPEUTICAL, AND TOXICOLOGICAL AGENT.

As a chemical agent, and from the manufacturing uses to which it is now put, salt is a most invaluable article from a scientific as well as from a commercial point of view. I will therefore draw the attention of my reader to its chemical properties; I will then allude to a few drugs which are partially derived from salt or the chloride of sodium; and will cursorily notice one great staple of commerce which owes the rapidity of manufacture to its sole agency, including some remarks on it as a poison.

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.

In France, though not hitherto, as far as I am aware, in Great Britain, several instances have occurred of severe sickness in particular localities, which have been traced to the adulteration of common salt with certain deleterious articles. In an investigation conducted by M. Guibourt some years ago, in consequence of some severe accidents which were presumed to have been produced apparently by salt in Paris and at Meaux, oxide of arsenic was detected; and this discovery was corroborated by MM. Latour and Lefrançois, who ascertained that the proportion of arsenic was sometimes a quarter of a grain per ounce. Another peculiar adulteration which was frequent was with the hydriodate of soda. At a meeting of the Parisian Academy of Medicine, held in December, 1829, an interesting report was read by MM. Boullay and Delens, subsequent to the inquiry by M. Sérullas, into the nature of a sample of salt which occasioned very extensive ravages. In the year 1829 various epidemic illnesses in several parishes were supposed to have originated from salt of bad quality, and in one month no less than 150 people in two parishes were attacked, some with nausea and pain in the stomach, slimy and bloody purging, some with tension of the abdomen, puffiness of the face, inflammation of the eyes, and œdema of the legs; and in some districts of the Marne one-sixth part of the inhabitants were affected in a similar manner. The salt being suspected, as it had an unusual odour somewhat like the effluvia of marsh land, it was analysed by M. Sérullas, and after him by MM. Boullay and Delens; the experiments of all three indicated the presence of one hundredth of its weight of hydriodate of soda, besides a small amount of free iodine. Owing to the discovery of arsenic by other experts in different samples of suspected salt, M. Sérullas repeated the analysis, but was unable to detect the slightest trace of that poison.

“M. Barruel states that he observed the occasional adulteration of salt with some hydriodate accidentally in 1824, while preparing experiments for Professor Orfila’s lectures. He also found it in two samples from different grocers’ shops in Paris. No satisfactory explanation has yet been given of the source of the adulteration with arsenic; but the presence of the hydriodate of soda has been traced to the fraudulent use of impure salt from kelp.”29

It will be as well for us to know what pure salt really consists of, to the composition of which I now draw the reader’s attention:

Composition of the Pure Chloride of Sodium.

	Atoms.	Eq. wt.	Per cent.	Ure.	Longchamps.
Sodium	1	23	39·3	39·98	39·767
Chlorine	1	35·5	60·7	60·02	60·233
	—	——	——	———	———
	2	58·5	100·0	100·00	100·000

MM. St. Claire Deville and Fouqué have shown that common salt can be resolved into its elements by the action of hot steam alone, which Lussa and other chemists had thought impossible.

Prof. Meyer, of Berne, has lately demonstrated by experiments on chlorine gas, that the assumption of its elementary character is an error, and that it is nothing more or less than the oxide of a metal which he calls murium. This discovery opens up an interesting question for physiological chemists to investigate; for if he is correct, chlorine is not an element, but is simply the oxide of a metal.