A model of a vessel set in a solution of sulphate of copper, and the bottom coated over with any cheap varnish, through which powdered black-lead or plumbago is mixed, is soon coated with a film of metallic copper when it is connected with the negative pole of the machine, the positive pole at the same time terminating in the solution, or attached to pieces of copper placed in it. These pieces of metal are continually dissolved, as equivalent quantities are taken up from the solution and deposited; and thus this is constantly preserved of its full saturated strength. By continuing the operation, the film of copper increases in thickness to any extent desired; and as it is produced over the whole surface prepared for its reception, the whole coppering of a ship may be thus laid on in one piece. If it be desirable to have the coating thicker in some parts than in others, as about the bows of a ship, this is effected by suspending sheets of connected with the positive wire opposite to these parts, and very near to them. As the particles of the metal are detached in the solution, they seem to hasten at once over to the nearest negative surface, and attach themselves there in as solid a form as they previously constituted in the original metal. Should there be any fear that the whole coating of copper might not have sufficient adherence, it is easily secured by nails; and but very few of these would be required compared with those now used for fastening the sheets by the usual method. copper Two other methods are also proposed of covering the bottom of a ship. One is, by leaving the old suit on, and coating upon this; and the other, by sheathing first with sheets of tin, and depositing the copper upon these cheap plates, either first from the cyanide solution, as the sulphate cannot be used for precipitating copper upon a surface of tin, or first a film of zinc upon the tin, and then of copper upon this. In the theory of these processes, as also in the operation on the small scale, no difficulty of any moment suggests itself. To carry out the operation in the large way, and actually sheath a vessel, a dock is required into which she can be floated, and from which the water can be let out. The bottom of the ship is then to be thoroughly cleaned, or if of wood, varnished over. The metallic solution is then to be let into the dock, and a large wire connected with the negative pole of the machine, passed around the vessel above the fluid. From this wire numerous strips of metal communicate with the surface to be coated; while another large wire from the positive pole terminates at any point in the liquid. By multiplying these wires, or by using heavy rods, the current from the machine is more rapidly produced, and the operation will go on the more expeditiously. Pieces of old copper, of any shape or size, are laid in the dock, and they, as they are dissolved, keep up the full strength of the solution. However impure these may be, nothing but the pure metal goes upon the vessel. The coating is thus of superior quality to the copper sheathing prepared in any other way. It is estimated that with a machine in steady operation for a week the whole bottom may be covered. The solution is then to be drawn off into another dock, water let in again, and the vessel be floated out. For convenience of operation, two docks would seem to be required, to be alternately used. In so extensive and novel an operation as this, it is reasonable to look for some difficulties in the first trials; but none suggest themselves of serious moment, unless it be the difficulty of ascertaining the thickness of copper deposited on different parts of the vessel, and of controlling this during the process. These, however, are merely mechanical obstacles, that are expected to yield to the ingenuity of the inventor of the machine. The cost of the operation, exclusive of the docks, is not likely to be much more than that of the weight of old copper used; for the same solution may continue in use with only slight waste, as it is transferred from one dock to another. In each transfer it is freed from the impurities that collect and settle in it. 175 Chemical Science. TIME REQUIRED BY COMPOUNDS FOR DECOMPOSITION. DR. WOODS, of Parsonstown, the discoverer of the Absorption of Heat by Decomposition, * has read to the British Association a paper in which the author may be said to have opened a new field in the natural philosophy of Chemistry. He shows that the time required by compounds for decomposition is definite and invariable, and similarly related under similar circumstances. This he proves by examining the quantity and rapidity of the current of electricity produced by a galvanic pair of zinc and platina-the zinc being acted on by sulphuric acid, the platina in a porous cell, surrounded successively by different solutions capable of decomposition, such as acidulated water, nitric acid, iodic acid, solution of sulphate of copper, solution of nitrate of silver, &c. Thus, there are several couples exactly the same, except in the matter of the fluid to be decomposed; and it was therefore evident that any difference in the amount of electricity passing with the several arrangements was due to the decomposition alone. In this way it was shown that every compound requires a definite and specific time to decompose, and that this period of time depends on the amount of heat absorbed by decomposition, -all compounds requiring the same time to absorb the same quantity of heat in decomposing, but differing in the amount absorbed. In this paper it is also shown that Faraday's opinion, that the metal of a galvanic couple most acted on is the positive one, is not correct. For if nitric and sulphuric acid are separated by a porous diaphragm, and a copper plate be placed in each, that in the sulphuric acid will be positive to the other, although not nearly so strongly acted on, because the decomposition of the water requires more time than that of nitric acid. In every case of galvanic arrangement decomposition influences the result as much as combination. It is also shown that the force of a galvanic pair can be precalculated from knowing the quantity of heat developed at the positive and absorbed at the negative end. In this way iodic acid was prejudged to be as efficient as nitric acid in the Grove's pair, and found to be so on experiment. The recognition of time in chemical changes assimilates them more closely than formerly with mechanical action.-(See the entire paper in the Proceedings of the British Association, 1857.) ARTIFICIAL GASTRIC JUICE. It has long been known, as matter of theory and experiment, to chemists and medical men, that it was possible to exhibit by artificial means some of the phenomena of digestion, and to dissolve portions of animal and other food in vessels maintained at a proper temperature, either by the gastric juice obtained from the stomach of an * See Year-Book of Facts, 1852, p. 168. animal killed shortly after a meal, or by a similar substance artificially prepared. But this theoretical knowledge has not, until very recently, been turned to practical account, to any considerable extent, in the treatment of those numerous and distressing forms of bodily disease and infirmity which arise from impaired powers of digestion. Dr. Landerer of Athens was, we believe, the first person who employed in medical practice an Artificial Gastric Juice, which he prepared from the stomach of the wolf; but even before that, rennet, a substance possessing somewhat similar properties, was occasionally used as a medicine in cases of dyspepsia. The systematic introduction, however, on a large scale, of a medicine capable of performing the functions which properly belong to the digestive organs, is due to Dr. Corvisart, a Parisian physician, and the results of its use appear sufficiently remarkable to merit general attention. Food, it must be observed, as introduced into the stomach, is not in a condition to enter the blood and be converted into the organized tissues of the body. It requires to undergo the process of digestion "that process, says Lehmann, "by virtue of which nutriment is transmitted, in accordance with chemical and physical laws, into the circulating system, for the renovation of those portions of the organs which have become effete;" the food being thereby, in the words of the same distinguished chemist, "reduced to a soluble state, or, generally speaking, to such a condition that it is capable of being absorbed into the mass of the juices of the animal body." Numerous experiments have been made, both as to the digestibility of various kinds of food, and as to the exact character of the process. Among the best known are those of Gosse, who had the power of inducing vomiting in his own person at will, and could thus recover for examination portions of food which had been exposed for some time to the action of the gastric juice-those of Beaumont, who employed a man whose stomach was easily accessible through a remarkable gunshot wound-and those of Schultz, who worked upon dogs and cats, which he killed at various intervals after feeding. Very great discrepancies exist between the results arrived at by the different investigators; nor have the experiments with artificial gastric fistulæ been much more satisfactory, so far as regards the degrees of digestibility of different aliments. But it is established that the modus operandi by which the change resulting from digestion is effected is one of those mysterious processes classed by chemists under the designation of catalysis, in which a substance, by virtue of the presence of some other body or bodies not themselves affected by what is taking place, becomes converted into something of which the chemical composition is identical with the original substance, but which nevertheless possesses very distinct and peculiar physical properties. The food, in fact, to use a term of organic chemistry, is converted into an isomeric variety of what it originally was; and one of the physical properties which it acquires by the change is its capability of absorption and assimilation by the proper secretive organs of the stomach and intestines. Until it undergoes this change, it can neither be absorbed nor assimilated, and is consequently not only useless, but injurious, and wholly incapable of supporting life. The solution of food of all kinds in the stomach is effected by the agency of gastric juice, which is, essentially, a combination of a substance called pepsin (literally, the cooking principle), with an acid-probably lactic acid, the pungent and disagreeable acid which imparts its peculiar flavour to sour milk. Much discussion has taken place among chemists as to whether or not other acids, such as acetic, hydrochloric, and phosphoric, are present in the active natural juice; but it appears certain, at all events, that in every case, unless it be one of absolute disease, lactic acid is present in such quantity as to communicate to the gastric juice a decided acid reaction. It attacks iron filings, and decomposes carbonate of soda. It is also matter of discussion whether the lactic acid be a primary and original constituent of the gastric juice, or whether it is produced in a more circuitous manner, the pepsin being secreted in a neutral state, and then acting as a ferment upon the amylaceous substances of the food, and so generating the acid. Thus much is certain, that the property of so acting, by causing fermentation, is inherent in the neutral substance-i.e., in pepsin without any lactic acid in composition with it—while pepsin in this neutral condition is destitute of digestive power. M. Boudault, of Paris, who alone has at present succeeded in preparing pepsin on a large scale, is of opinion that the secretion is neutral. The question is of consequence, for if it be so, the part played by the saliva in the whole machinery of digestion assumes additional importance, as we must then conclude that one of its constituents (diastase) is employed in the stomach to convert the starchy matter of the food into grape sugar; and this, in its turn, is converted by the pepsin into lactic acid, without the aid of which, pepsin could not perform its appropriate functions. Whatever be the precise reaction of pepsin, one fact is clear-it is the principal and indispensable element in producing the change involved in the operation of digestion. Remove the pepsin, and all the other secretions are powerless-acidulate slightly a solution which contains (according to Wasmann) but one sixty-thousandth part of pepsin, and in a few hours it will dissolve coagulated albumen. Hence if, in cases of impaired digestive power, pepsin can be introduced, even in very small quantities, into the stomach at the time of taking food, the operations of nature will be wonderfully facilitated. So long ago as 1834, it was proved by Eberle that the gastric juice retains its power after removal from the body; but it is an excessively nauseous fluid, and can only be obtained in any available quantities by the destruction of a great number of animals. It contains as much as 97 per cent. of water, about 1.75 of salts, and only 1.25 of pepsin; and if, therefore, the pepsin could be obtained distinct from these diluting elements, a great point would be gained, and its administration rendered comparatively easy. Experiments M made by Schwann established the important fact that it is only the glandular structure of the stomach which contains a digestive fluid from which the pepsin may be precipitated; and this led to the preparation of pepsin in the manner now used by M. Boudault. A number of rennet bags-commonly used in making cheese, and which are the fourth stomachs of the ruminants-are turned inside out, very gently washed, and the mucous membrane, which contains the follicles whereby the juice is secreted, scraped off. It is reduced to a pulp, steeped for twelve hours in cold distilled water, and acetate of lead (sugar of lead) added. This precipitates the pepsin; and the precipitate is treated with sulphuretted hydrogen, which separates the lead as sulphuret, and leaves the pepsin in solution. It is then filtered and evaporated to a syrup, or even to a dry powder, at a low heat; for it happens very curiously that, if exposed to a heat of more than 120° F., it loses all power of digestion. In either of these conditions, however, it is very liable to decomposition if exposed to air, is excessively deliquescent, and the taste and smell are repulsive, resembling those of bad broth. The syrupy solution is therefore mixed with starch, and the mixture carefully dried. It then forms a grey powder, like coarse flour, and by addition of starch or pepsin, as the case may require, can be brought to an uniform standard of strength; and it is then fit for medicinal use, either by itself or mixed with muriate of morphia, strychnia, salts of iron, or other reagents, which do not affect its digestive properties. Thus prepared, pepsin can be taken with the greatest ease, either in water, or between slices of bread, or in any other simple manner; and according to M. Boudault-from whose communication to the Imperial Academy of Medicine some of the foregoing facts have been taken-and to Dr. Ballard, who has introduced it into London practice, it is capable in every way of representing and replacing the normal gastric juice of the human body. Some very curious instances are mentioned by Dr. Ballard, whose character and position render him a witness above suspicion, and whose cases are recorded in sufficient numbers to preclude the possibility of the results being attributable to any accidental circumstances. Perhaps the most remarkable case is that of a lady, sixty-six years of age, who for four years had suffered pain which she had no words to describe," for three or four hours after every meal. The natural consequences were, excessive prostration and complete disgust for food; and she had for many weeks limited herself to four rusks and a little milk and beef-tea per diem. The first day pepsin was used, she ate, with ease and enjoyment, a mutton chop-though, on the day before, she had endured intense agony for no less than five hours after her ordinary meal. In a few days she ate pretty freely, and gradually improved, and at length was able to give up the pepsin entirely, to eat without pain, and walk some miles without fatigue. (Dr. Ballard, on Artificial Digestion, p. 30.) The pepsin appears from this and many other recorded cases, not only to act per se on the food, but to restore the lost activity of the secretive organs. The importance of such a result, and the value of the remedy, can |