[2]. River-water is in general purer than spring-water; as the neutral salts washed down from the earth decompose each other, except perhaps the marine salt; and the earths, with which spring-water frequently abounds, is precipitated; yet it is not improbable, that the calcareous earth dissolved in the water of many springs may contribute to our nourishment, as the water from springs, which contain earth, is said to conduce to enrich those lands, which are flooded with it, more than river water.
[3]. Many arguments seem to shew, that calcareous earth contributes to the nourishment of animals and vegetables. First because calcareous earth constitutes a considerable part of them, and must therefore either be received from without, or formed by them, or both, as milk, when taken as food by a lactescent woman, is decomposed in the stomach by the process of digestion, and again in part converted into milk by the pectoral glands. Secondly, because from the analogy of all organic life, whatever has composed a part of a vegetable or animal may again after its chemical solution become a part of another vegetable or animal, such is the general transmigration of matter. And thirdly, because the great use of lime in agriculture on almost all kinds of soil and situation cannot be satisfactorily explained from its chemical properties alone. Though these may also in certain soils and situations have considerable effect.
The chemical uses of lime in agriculture may be, 1. from its destroying in a short time the cohesion of dead vegetable fibres, and thus reducing them to earth, which otherwise is effected by a slow process either by the consumption of insects or by a gradual putrefaction. Thus I am informed that a mixture of lime with oak bark, after the tanner has extracted from it whatever is soluble in water, will in two or three months reduce it to a fine black earth, which, if only laid in heaps, would require as many years to effect by its own spontaneous fermentation or putrefaction. This effect of lime must be particularly advantageous to newly inclosed commons when first broken up.
Secondly, lime for many months continues to attract moisture from the air or earth, which it deprives I suppose of carbonic acid, and then suffers it to exhale again, as is seen on the plastered walls of new houses. On this account it must be advantageous when mixed with dry or sandy soils, as it attracts moisture from the air above or the earth beneath, and this moisture is then absorbed by the lymphatics of the roots of vegetables. Thirdly, by mixing lime with clays it is believed to make them less cohesive, and thus to admit of their being more easily penetrated by vegetable fibres. A mixture of lime with clays destroys their superabundancy of acid, if such exists, and by uniting with it converts it into gypsum or alabaster. And lastly, fresh lime destroys worms, snails, and other insects, with which it happens to come in contact.
Yet do not all these chemical properties seem to account for the great uses of lime in almost all soils and situations, as it contributes so much to the melioration of the crops, as well as to their increase in quantity. Wheat from land well limed is believed by farmers, millers, and bakers, to be, as they suppose, thinner skinned; that is, it turns out more and better flour; which I suppose is owing to its containing more starch and less mucilage. In respect to grass-ground I am informed, that if a spadeful of lime be thrown on a tussock, which horses or cattle have refused to touch for years, they will for many succeeding seasons eat it quite close to the ground.
One property of lime is not perhaps yet well understood, I mean its producing so much heat, when it is mixed with water; which may be owing to the elementary fluid of heat consolidated in the lime. It is the steam occasioned by this heat, when water is sprinkled upon lime, if the water be not in too great quantity or too cold, which breaks the lime into such fine powder as almost to become fluid, which cannot be effected perhaps by any other means, and which I suppose must give great preference to lime in agriculture, and to the solutions of calcareous earth in water, over chalk or powdered limestone, when spread upon the land.
[4]. It was formerly believed that waters replete with calcareous earth, such as incrust the inside of tea-kettles, or are laid to petrify moss, were liable to produce or to increase the stone in the bladder. This mistaken idea has lately been exploded by the improved chemistry, as no calcareous earth, or a very minute quantity, was found in the calculi analysed by Scheel and Bergman. The waters of Matlock and of Carlsbad, both which cover the moss, which they pass through, with a calcareous crust, are so far from increasing the stone of the bladder or kidnies, that those of Carlsbad are celebrated for giving relief to those labouring under these diseases. Philos. Trans. Those of Matlock are drank in great quantities without any suspicion of injury; and I well know a person who for above ten years has drank about two pints a day of cold water from a spring, which very much incrusts the vessels, it is boiled in, with calcareous earth, and affords a copious calcareous sediment with a solution of salt of tartar, and who enjoys a state of uninterrupted health.
[V]. [1]. As animal bodies consist much both of oxygen and azote, which make up the composition of atmospheric air, these should be counted amongst nutritious substances. Besides that by the experiments of Dr. Priestley it appears, that the oxygen gains admittance into the blood through the moist membranes of the lungs; and seems to be of much more immediate consequence to the preservation of our lives than the other kinds of nutriment above specified.
As the basis of fixed air, or carbonic acid gas, is carbone, which also constitutes a great part both of vegetable and animal bodies; this air should likewise be reckoned amongst nutritive substances. Add to this, that when this carbonic acid air is swallowed, as it escapes from beer or cyder, or when water is charged with it as detruded from limestone by vitriolic acid, it affords an agreeable sensation both to the palate and stomach, and is therefore probably nutritive.
The immense quantity of carbone and of oxygen which constitute so great a part of the limestone countries is almost beyond conception, and, as it has been formed by animals, may again become a part of them, as well as the calcareous matter with which they are united. Whence it may be conceived, that the waters, which abound with limestone in solution, may supply nutriment both to animals and to vegetables, as mentioned above.