We know, also, fluosilicic acid and fluoboric acids. If to these we add fulminic acid, and the various sulphur acids already investigated, we may state, without risk of any excess, that the number of acids at present known to chemists, and capable of uniting to bases, exceeds a hundred.
The number of alkaline bases is not, perhaps, so great; but it must even at present exceed seventy; and it will certainly be much augmented when chemists turn their attention to the subject. Now every base is capable of uniting with almost every acid,[9] in all probability in at least three different proportions: so that the number of salts which they are capable of forming cannot be fewer than 21,000. Now scarcely 1000 of these are at present known, or have been investigated with tolerable precision. What a prodigious field of investigation remains to be traversed must be obvious to the most careless reader. In such a number of salts, how many remain unknown that might be applied to useful purposes, either in medicine, or as mordants, or dyes, &c. How much, in all probability, will be added to the resources of mankind by such investigations need not be observed.
The animal and vegetable kingdoms present a still more tempting field of investigation. Animal and vegetable substances may be arranged under three classes, acids, alkalies, and neutrals. The class of acids presents many substances of great utility, either in the arts, or for seasoning food. The alkalies contain almost all the powerful medicines that are drawn from the vegetable kingdom. The neutral bodies are important as articles of food, and are applied, too, to many other purposes of first-rate utility. All these bodies are composed (chiefly, at least) of hydrogen, carbon, oxygen, and azote; substances easily procured abundantly at a cheap rate. Should chemists, in consequence of the knowledge acquired by future investigations, ever arrive at the knowledge of the mode of forming these principles from their elements at a cheap rate, the prodigious change which such a discovery would make upon the state of society must be at once evident. Mankind would be, in some measure, independent of climate and situation; every thing could be produced at pleasure in every part of the earth; and the inhabitants of the warmer regions would no longer be the exclusive possessors of comforts and conveniences to which those in less favoured regions of the earth are strangers. Let the science advance for another century with the same rapidity that it has done during the last fifty years, and it will produce effects upon society of which the present race can form no adequate idea. Even already some of these effects are beginning to develop themselves;—our streets are now illuminated with gas drawn from the bowels of the earth; and the failure of the Greenland fishery during an unfortunate season like the last, no longer fills us with dismay. What a change has been produced in the country by the introduction of steam-boats! and what a still greater improvement is at present in progress, when steam-carriages and railroads are gradually taking the place of horses and common roads. Distances will soon be reduced to one-half of what they are at present; while the diminished force and increased rate of conveyance will contribute essentially to lower the rest of our manufactures, and enable us to enter into a successful competition with other nations.
I must say a few words upon the application of chemistry to physiology before concluding this imperfect sketch of the present state of the science. The only functions of the living body upon which chemistry is calculated to throw light, are the processes of digestion, assimilation, and secretion. The nervous system is regulated by laws seemingly quite unconnected with chemistry and mechanics, and, in the present state of our knowledge, perfectly inscrutable. Even in the processes of digestion, assimilation, and secretion, the nervous influence is important and essential. Hence even of these functions our notions are necessarily very imperfect; but the application of chemistry supplies us with some data at least, which are too important to be altogether neglected.
The food of man consists of solids and liquids, and the quantity of each taken by different individuals is so various, that no general average can be struck. I think that the drink will, in most cases, exceed the solid food in nearly the proportion of 4 to 3; but the solid food itself contains not less than 7-10ths of its weight of water. In reality, then, the quantity of liquid taken into the stomach is to that of solid matter as 10 to 1. The food is introduced into the mouth, comminuted by the teeth, and mixed up with the saliva into a kind of pulp.
The saliva is a liquid expressly secreted for this purpose, and the quantity certainly does not fall short of ten ounces in the twenty-four hours: indeed I believe it exceeds that amount: it is a liquid almost as colourless as water, slightly viscid, and without taste or smell: it contains about 3/1000 of its weight of a peculiar matter, which is transparent and soluble in water: it has suspended in it about 1·4/1000 of its weight of mucus; and in solution, about 2·8/1000 of common salt and soda: the rest is water.
From the mouth the food passes into the stomach, where it is changed to a kind of pap called chyme. The nature of the food can readily be distinguished after mastication; but when converted into chyme, it loses its characteristic properties. This conversion is produced by the action of the eighth pair of nerves, which are partly distributed on the stomach; for when they are cut, the process is stopped: but if a current of electricity, by means of a small voltaic battery, be made to pass through the stomach, the process goes on as usual. Hence the process is obviously connected with the action of electricity. A current of electricity, by means of the nerves, seems to pass through the food in the stomach, and to decompose the common salt which is always mixed with the food. The muriatic acid is set at liberty, and dissolves the food; for chyme seems to be simply a solution of the food in muriatic acid.
The chyme passes through the pyloric orifice of the stomach into the duodenum, the first of the small intestines, where it is mixed with two liquids, the bile, secreted by the liver, and the pancreatic juice, secreted by the pancreas, and both discharged into the duodenum to assist in the further digestion of the food. The chyme is always acid; but after it has been mixed with the bile, the acidity disappears. The characteristic constituent of the bile is a bitter-tasted substance called picromel, which has the property of combining with muriatic acid, and forming with it an insoluble compound. The pancreatic juice also contains a peculiar matter, to which chlorine communicates a red colour. The use of the pancreatic juice is not understood.
During the passage of the chyme through the small intestines it is gradually separated into two substances; the chyle, which is absorbed by the lacteals, and the excrementitious matter, which is gradually protruded along the great intestines, and at last evacuated. The chyle, in animals that live on vegetable food, is semitransparent, colourless, and without smell; but in those that use animal food it is white, slightly similar to milk, with a tint of pink. When left exposed to the air it coagulates as blood does. The coagulum is fibrin. The liquid portion contains albumen, and the usual salts that exist in the blood. Thus the chyle contains two of the constituents of blood; namely, albumen, which perhaps may be formed in the stomach, and fibrin, which is formed in the small intestines. It still wants the third constituent of blood, namely, the red globules.
From the lacteals the chyle passes into the thoracic duct; thence into the left subclavian vein, by which it is conveyed to the heart. From the heart it passes into the lungs, during its circulation through which the red globules are supposed to be formed, though of this we have no direct evidence.