Pharmacologia / Fourth American, from the Seventh London Edition

by John Ayrton Paris

Gignitur Ægypto in Medio.”

[384]. Dr. Percival observes that bricks harden the softest water, and give it an aluminous impregnation; the common practice of lining wells with them, is therefore very improper, unless they be covered with cement.

[385]. The same strumous affection occurs at Sumatra, where ice and snow are never seen; while, on the contrary, the disease is quite unknown in Chili and Thibet, although the rivers of these countries are chiefly supplied by the melting of the snow with which the mountains are covered. The trials of Captain Cook, in his voyage round the world, prove the wholesomeness of Ice water beyond a doubt; in the high southern latitudes he found a salutary supply of fresh water in the ice of the sea; “this melted ice,” says sir John Pringle, “was not only sweet but soft, and so wholesome as to shew the fallacy of human reasoning unsupported by experiments.”

[386]. I take this opportunity of observing that I have made analyses of several of those springs in Cornwall, which have from time immemorial enjoyed a reputation in the neighbourhood for curing diseases, amongst which were the waters of Holywell, so named from its supposed virtues, and those of Permiscen Bay, equally extolled for their medicinal qualities. But I have only been able to detect minute quantities of carbonate of lime, derived from infiltration through banks of calcareous sand. See Transactions of the Royal Geological Society of Cornwall, Vol. I.

[387]. See “Remarks on the Pump water of London,” by W. Heberden, M. D. in the 1st. vol. of the Medical Transactions; also, Acad. Royale des Scienc. 1700, Hist. pag. 58. Perrault Vitruve. L. VIII. c. 5.

[388]. I am informed by a respectable chemist in this town, that he sells a large quantity of alum for this very purpose, as well as to publicans for the sake of clearing their spirituous liquors; for the same end, we are told, that the wine merchants in Paris put into each cask of wine as much as a pound of alum.

[389]. This is particularly the case with respect to the water of the River Thames; for as it contains but a small proportion of saline matter, it is remarkably soft, although it holds suspended mud, and vegetable and animal debris, which occasion it to undergo a violent change on being kept: a large volume of carburetted and sulphuretted hydrogen gases is evolved, and it becomes black and insufferably offensive; upon racking it off however into large earthen vessels, and exposing it to the air, it gradually deposits a quantity of black slimy matter, and becomes as clear as crystal, and perfectly sweet and palatable, and is exceedingly well adapted for sea store. “The New River Water” contains a small proportion of muriate of lime, carbonate of lime, and muriate of soda; it differs also in its gaseous contents: 100 cubic inches of New River Water contain 2·25 of carbonic acid, and 1·25 of common air, whereas the water of the Thames contains rather a large quantity of common air, and a smaller proportion of carbonic acid.

[390]. The law which determines such combinations has been investigated with singular ingenuity and success by Dr. Murray, (Transactions of the Royal Society of Edinburgh, 1816). Berthollet had already established the important fact, that combinations are often determined by the force of cohesion, in such a manner, that in principles acting on each other, those on which this force operates most powerfully, in relation to the fluid which is the medium of action, are combined together; hence from a knowledge of the solubility of the compounds which substances form, we may predict what combinations will be established when they act on each other, those always combining which form the least soluble compounds. It is for the extension of these views, and for the useful application of them, that we are indebted to Dr. Murray, who justly observes that if the force of cohesion can so far modify chemical attraction, as to establish among compound salts dissolved in any medium, those combinations whence the least soluble compound are formed, we are entitled to conclude that the reverse of this force, i. e. the power of a solvent, may produce the opposite effects, or cause the very reverse of these combinations to be established, so that in a concentrated medium the least soluble will be formed, and in a dilute one, the more soluble compounds will be established. Hence follows the simple rule by which the actual state in which saline bodies exist in a solution may be determined, viz. that in any fluid containing the elements of compound salts, the binary compounds existing in it will be generally those which are most soluble in that fluid, and the reverse combinations will only be established by its concentration favouring the influence of cohesion. It appears that by simply evaporating a saline solution we may produce changes in its composition, and obtain products which never existed in its original state of dilution; thus, suppose muriate of magnesia and sulphate of soda to be dissolved in water, as is actually the case in the water of the ocean, and the solution to be concentrated by evaporation from heat; the combinations of sulphate of magnesia and muriate of soda, being on the whole less soluble in water, this circumstance of inferior solubility, or the force of cohesion thus operating, actually determines the formation of these compounds; and the production of sulphate of magnesia from the bittern is to be explained upon this principle. Since it appears therefore that the influence of solubility is most important, temperature, to whose dominion it is under all circumstances subject, must necessarily be alike powerful; let us exemplify this fact by the action of the very salts under consideration; it has been just stated that muriate of magnesia and sulphate of soda decompose each other in a concentrated solution at a high temperature, producing muriate of soda and sulphate of magnesia, but at temperatures below 32° the reverse actually takes place, muriate of soda and sulphate of magnesia reacting, and being converted into sulphate of soda and muriate of magnesia; a fact evidently owing to the relation of the solubility of these salts to temperature. Muriate of soda has its solubility scarcely altered, either by heat or cold; sulphate of soda is, in these respects, completely the reverse; hence at an elevated temperature, muriate of soda is the least, and sulphate of soda the most soluble salt, whilst at a low temperature, the reverse of this happens. All the circumstances of this investigation are most interesting; the medical practitioner will at once perceive its importance, as enabling him to appreciate the real nature of saline solutions, and even in many instances to preserve their identity. See Aquæ Minerales.

[391]. There is a precaution respecting the preservation of these waters for analysis with which the chemist ought to be acquainted; it will be fully explained by the relation of the following anecdote. M. Wurza, on examining some bottles of Chalybeate water, could detect no signs of iron in them, and on seeking for the cause of this circumstance, he discovered it in the astringent nature of the corks which had combined with the metallic substance, and abstracted it from the water.

[392]. The Mineral Springs in the United States more especially deserving of notice, are those of Saratoga and Ballston in the State of New-York, and of Schooley’s Mountain in New-Jersey. Of the two first, various analyses have been published by different chemists, but with so little uniformity of result as to leave their true chemical character still in a state of uncertainty. An account of these discrepancies may be seen in the New-England Journal of Medicine and Surgery for 1817. As the analyses of Dr. Steel appear upon the whole to be most satisfactory, we shall quote them. One gallon of the water was the quantity used in the experiments.