6. Lake Water. Aqua ex Lacu, is a collection of rain, spring, and river waters, contaminated with various animal and vegetable bodies, which from its stagnant nature have undergone putrefaction in it.
7. Marsh Water. Aqua ex Palude being the most stagnant is the most impure of all water, and is generally loaded with decomposing vegetable matter.
To what extent the impurities of water are capable of influencing its salubrity, has been a subject of interesting inquiry from the age of Hippocrates to the present day. To many of these natural contaminations, too much importance has been certainly attached; it is an affected refinement to suppose that the presence of minute portions of such earthy and calcareous salts, as generally occur in solution, can impart any noxious quality to water;[[386]] whilst on the contrary, animal and vegetable impurities, or earthy bodies in a state of mechanical suspension, cannot fail to prove injurious, and must be regarded as the true “SCELERA AQUARUM.” Guided by false analogies many have supposed that they recognised the origin of all calcareous diseases in the earthy impurities of water; the researches however of chemistry have removed this delusion, by demonstrating that the substances found in water never enter into the composition of urinary calculi.[[387]] Metallic and other accidental contaminations are necessarily highly injurious, and the water in which their presence is suspected, should be submitted to the most careful examination.
For the purification and preservation of water numerous methods have been adopted; the mechanical impurities may be removed by filtration, which is performed through porous stones, or alternate layers of sand or charcoal; muddy water may be also cleared by adding a few grains of alum to each pint,[[388]] and in that proportion, the water is not rendered in the least disagreeable: when water has contracted a putrid smell, it may be rendered sweet by agitating it with a small portion of magnesia, or with black oxide of manganese, in the proportion of 1½ parts to 250 parts of water. Dr. Black observes that nitrate of silver, which is one of the most antiseptic substances known, will preserve water from putrefaction for ever, and that it may at any time be separated therefrom in a few minutes by adding a small lump of common salt; this fact in itself is curious, but the experiment is too hazardous to be recommended. Dr. Alston prefers lime, as a preservative of the water, and proposes to remove it by the addition of a carbonate of magnesia; Dr. Henry has however found that it is more economically precipitated by the introduction of a current of carbonic acid into the cask. As that peculiar property of water which is termed hardness, generally depends upon the presence of sulphate of lime, the addition of an alkaline carbonate twenty-four hours previous to its being used, will be found to restore it, or if it should depend upon supercarbonate of lime, long ebullition without any addition will be found sufficient for its cure.
Water when kept for a long time in casks, especially on long voyages, is partially decomposed, and a volume of carburetted hydrogen is evolved,[[389]] imparting to such water the peculiar smell and taste which characterise it; this decomposition may in a great degree be obviated by charring the interior of the water casks; it is, however, prevented in the Navy by substituting iron tanks for wooden vessels. In Pharmacy it ought to be remembered that whenever common water is employed it should not be hard; filtered rainwater maybe recommended as the most eligible on such occasions.
AQUA DESTILLATA. L.E.D. Distilled Water.
Qualities. Taste, vapid from the absence of air, and slightly empyreumatic in consequence probably of the presence of a small quantity of extractive matter which has undergone partial decomposition; a fluid-ounce weighs 454½ grains. Medicinal Use. In extemporaneous prescriptions, distilled water should be always ordered whenever the formula contains any of the following substances:—Acidum Sulphuricum; Acidum Citricum; Antimonium Tartarizatum; Argenti Nitras; Cuprum Ammoniatum; Ferrum Tartarizatum; Hydrargyri Oxy-murias; Liquor Ammoniæ; Liquor Plumbi Sub-Acetatis; Liquor Potassæ; Plumbi Acetas; Solutio Muriatis Barytæ; Vinum Ferri; Zinci Sulphas; Ferri Sulphas. Distilled water ought also to be employed in preparations where much water is evaporated, as in the formation of extracts, since the residual matter of common water will remain mixed with the product of the process, and uselessly add to its bulk, or even in some cases produce in it chemical changes; unless however under such circumstances, common water purified by filtration should be ordered, as the air which it contains imparts to it a pleasant and sprightly flavour. In making infusions or decoctions, it is very important that the water should be free from those impurities which impart to it hardness, and which render it a far less powerful solvent of vegetable matter, nor indeed can resinous substances be mixed with such water, even when assisted by a mucilaginous medium. On which account, in prescribing emulsions, it may perhaps be prudent to direct the employment of distilled water. Tests of its Purity. Its transparency ought not to be disturbed by the addition of nitrate of silver, or muriate of baryta.
AQUA MARINA. Sea Water.
Until the late able researches of Dr. Murray, we possessed but an imperfect knowledge of the composition of sea water; it is not therefore surprising that the analysis performed by different chemists should be found to be so materially at variance; the true cause of such discordance is now easily understood, for it appears, that in the examination of a mineral water or any compound saline solution, the substances obtained from it are not necessarily the original ingredients, but frequently the products of new combinations established by the operation of analysis, and that consequently the nature of the result obtained may vary according to the modes in which such analysis has been conducted, or even according to the degree of dilution in which the saline substances exist.[[390]] The elements of the salts contained in a pint of sea water are Lime 2·9, Magnesia 14·8, Soda 96·3, Sulphuric Acid 14·4, Muriatic Acid 97·7, total 226·1 grains, and supposing these elements to be combined in the modes which Dr. Murray’s views appear to establish, the saline contents of a pint of sea water may be expressed as follows, Muriate of Soda 159·3, Muriate of Magnesia 35·5, Muriate of Lime 5·7, Sulphate of Soda 25·6 grains, total 226·1 grains; besides such saline contents, it is contaminated with various animal and vegetable bodies, in consequence of which it becomes, when long kept, highly offensive; it ought also to be stated that Dr. Wollaston has discovered the presence of a minute proportion of potass in sea water; and Dr. Marcet has more lately detected ammonia in combination with muriatic acid. Medicinal Use. As a cathartic, a pint is the ordinary quantity, which should be taken in the morning, at two doses, with an interval of half an hour between each; this quantity contains half an ounce of purgative salt, of which about three-fourths are muriate of soda, but it is much more active than a similar portion of any artificial combination. In procuring sea water for medicinal purposes, there is a precaution, the importance of which experience has suggested to me, that it be not hastily drank on the beach, before the particles of sand, with which under such circumstances it is generally mixed, are allowed to subside; from the neglect of this precaution I have witnessed serious consequences. The most important advantages of sea water are derived from its external use as a bath.
AQUÆ DESTILLATÆ. L.D.