2 (ENGLISH METHOD.) SULPHURIC acid is a compound of the two simple substances oxygen and sulphur, in the proportion, by weight, of three oxygen and two sulphur. As it is usually met with in commerce, it is in a liquid form, which is owing to the water combined with it, and for which it has a very strong affinity. At Nordhausen, in Germany, a very much concentrated sulphuric acid is obtained from the distillation of green vitriol, and if this, put into a glass retort, be distilled by a mode rate heat, and received into a vessel surrounded by ice, sulphuric acid is obtained in a solid state. It is tough, and resembles asbestos in its appearance. When exposed to the air it fumes, and gradually flies off in vapour. In the solid state its properties are not known, and it is put to no use; but when united with water, in various proportions, it is perhaps the most useful of all the agents employed by the chemist, and more used in the arts and manufactories than any other acid except the acetic. We propose, therefore, in the present paper to give a short account of the mede of manufacturing it on a large scale, as now carried on in various ✓ parts of France and England. The diluted sulphuric acid, or the hydrate of sulphuric acid, as it is called, has been known since the R latter end of the sixteenth century, and up to the early part of the 18th it was wholly obtained from sulphate of iron, or the green vitriol of commerce; and hence sulphuric acid was improperly called oil of vitriol. Dr. Ward then introduced the method of obtaining it by burning sulphur and nitre; and enjoyed the monopoly of this manufacture for several years. In 1746, Dr. Roebuck, an eminent and scientific physician, began at Birmingham the practice of burning the sulphur, and receiving the product in leaden chambers. That reduced the price of the article one-fourth, and allowed it to be employed for a variety of purposes from which it was before excluded by its great cost. Since that time manufactories of sulphuric acid on, this principle have been established, on an extensive scale, in several parts of the kingdom. In England it has not yet been settled what dimensions are the best for the leaden chambers; the manufacturers construct them according to their convenience; and Mr. Parkes* (whose account we are now abridging,) mentions one in Lancashire, who built several rooms 120 by 40 feet, and 20 feet high. Whatever may be the size of the chambers, the process is conducted in the following manner Common brimstone, coursely ground, is mix *"Chemical Essays," vol. I. p. 484. 1 ed with saltpetre in the proportion of eight pounds of the former to one of the latter; and the mixture is spread on leaden or iron plates, placed on stands of lead within a chamber wholly lined with lead and covered at the bottom with a thin sheet of water. About one pound of the mixture is allowed to every three hundred cubical feet of atmospherical air contained in each chamber; and when a charge in this proportion has been placed in one of them, the mixture is lighted by means of a hot iron, and the door is closed. The combustion of the two substances, if well mixed, continues about forty minutes. In about three hours the gas is all condensed, and the chamber is thrown open to admit atmospheric air, and prepare it for another burning. The plates are again charged, and the same process is repeated every four hours, without intermission either by day or night, until the water at the bottom of the chamber is thought to be sufficiently acidified. This is judged of by the acid turning black, when it is drawn off by means of a syphon into a reservoir of lead It is then concentrated by the action of heat in leaden boilers, until it has acquired such a specific gravity as best suits the manufacturer's purpose. It is afterwards boiled in glass retorts till all the sulphurous and nitric acids are driven off, and it is fit for the market. The necessity for the concentration by means of heat, arises from the water, after it has taken up a certain quantity, refusing to absorb the acid so readily as at first. Care, too, must be taken when the acid is in the leaden boiler that it be not too much concentrated, for the boiling point of much concentrated acid, and the melting point of lead are so near to each other, that the leaden boiler may be destroyed. Some manufacturers remove it at once into the glass retorts, and do not steam it in lead, which prevents the acid combining with so large a quantity of this metal. Lately, too, platinum alembics, placed within pots of cast iron of a corresponding shape and capacity, 2 have been substituted for the glass retorts, and h have been found to save fuel and quicken the progress of concentration. Mr. Parkes mentions that he had a platinum vessel constructed for rectifying sulphuric acid some years ago: it cost some hundred pounds, but answered the purpose perfectly well. The sulphuric acid of commerce always contains sulphate of potash, derived from the nitre, and sulphate of lead derived from the lead used in the process. In order that this method u should succeed, it is essential ygen be present to maintain the combustion, that the chamber do not allow the volatile matter which arises to escape, and that water be present to absorb it. For a long time, however, the rationale of this method was involved in doubt and obscurity. It was found that 100 parts of nitre, containing only 391 of oxygen, when combined with the requisite quantity of sulphur, pro-ge duces a quantity of sulphuric acid, containing 1200 parts of oxygen Moreover, after the combustion of the sulphur, the residuary salts contain nearly as much oxygen as was originally contained in the nitre 01 and the 1200 parts of oxygen in the acid could not be accounted for, At length Messrs. Clement and Desormes, two manufacturing French chemists, succeeded in explaining this circumstance, and their explanation has since been confirmed by Mr. Dalton and Sir H. Davy. They supposed that the burning sulphur, taking from the ot nitre a portion of its oxygen, forms sulphuric acid, which, uniting with the base of the nitre, or potash, displaces nitric and nitrous acids in vapour, which is decom-007 posed by the sulphurous gas into nitrous gas or deutoxide of azote, Being naturally only a little heavierď than air, and being then rarefied by mo the heat, the nitrous gas rises to the roof of the chamber, and there coming into contact with atmo-0,2 spherical air, by means of a hole, n and without which the manufactu-l & rers found that the acidification would not go on, forms n nitrous acid 19891 vapour, which, being a heavy body, immediately precipitates on the sulphurous flames. Sulphuric acid and nitrous gas are again formed, and the latter again mounts for a new charge of oxygen, again to redescend and transfer it to the sul phur. Sir H. Davy has since shown that water is necessary to the mutual action of sulphurous gas, and nitrous gas, and that unless this fluid be present the process does not go on. With this additional fact it would appear that a small volume of nitrous vapour, by its alternate and frequent changes into oxide and acid, is capable of acidifying a great quantity of sulphur. We shall now describe the plate, which may serve to give our readers some idea of a sulphuric acid manufactory. We have borrowed it from the valuable work of Mr. Parkes, entitled "Chemical Essays." It is the representation of the yard of a sulphuric acid manufactory, walled round with all its requisite buildings: AAAA are chambers of combustion made with sheet lead; B, the main reservoir, also of lead, to contain the acid drawn from the chambers; C, a trough lined with lead, to convey the acid to the reservoir. The acid is drawn by a syphon from the chamber into the trough; D, a pump to supply the leaden boilers, EEEEE, with acid from the reservoir. These boilers are for concentrating the acid. They are placed under a roof supported by pillars at the dots, marked F. G. the reservoir for the concentrated acid, provided with a close cover to prevent the acid absorbing moisture; H is the room where the acid is still further concentrated by boiling in glass retorts; I, is an open shed, supported on pillars, for packing, &c.; K, a warehouse; L, counting rooms; MN, store rooms; 0, pounding room; P, stable; Q, small laboratory; R, entrance; S, coal store; T, pump for supply ing water; U, another pump; W, a large storehouse. (French Method in our next.) ON RESPIRATION, AND THE PRODUCTION OF ANIMAL HEAT. IN our 19th Number we published a little article, showing the effect of evaporation in preserving bodies, animals as well as others, at about blood heat, when every thing around them is at a much higher temperature. This is a chemical phenomenon; for every thing relative to the production of heat falls into the department of che mistry. Admitting that evaporation is sufficient for this when the body is in a medium considerably hotter than itself, the question occurs, What is it which preserves the human body and other animals at a high temperature when they exist in a much colder medium? Is this, too, a chemical phenomenon? We believe it is; but many of our readers may perhaps be disposed to doubt the fact. They constantly experience sensations of heat and cold, in every part of their body, and may therefore not exactly comprehend what we mean, or doubt our assertion. We do not at present allude to what they feel, but to the state of the thermometer when brought into contact with the human body. We beg them, therefore, for the moment, to forget the piercing winter's blast, and the melting summer's sun, and to think only of the expansion of mercury. It is, then, a very remarkable fact, which has been verified by repeated observations, that when a thermometer is placed under the armpit, under the tongue, or in any position so as to be affected only by the heat of the body, it always.. stands, in all climates, in all situations, and with whatever person the experiment is made, about the same height, or about the 98th degree. There is some little variation from this. The temperature of infants is somewhat lower; and there are cases of disease recorded, particularly one by Dr, Prevost, of Geneva, in which the temperature of the body was much higher. But in general the mercury stands at the same mark. "Among the pheno spiration in contributing to the production of animal heat has been generally admitted, though his theory of respiration has been disputed. That the two are intimately connected, is by no man now denied; and therefore our readers will see the propriety of our having here united them in one article, meaning, as briefly as possible, to give an outline of both. mena," says M. Despretz, a French author, to whose paper, "On animal heat," a prize was awarded by the French Institute, in 1823, "which the study of physiology offers to our view, there is no one more capable of exciting our attention, than the extraordinary property with which man and all hot blooded animals are endowed, of preserving a temperature nearly equal, though the media around There have been various theothem undergo continual variations. ries of the process of respiration; From the very beginning of expe- but without discussing them, we rimental physiology, enlightened shall merely state the best estainquirers, such as Haller, Hunter, blished facts. The atmosphere is Bichat, Le Gallois, Dr. J. Davy, composed by measure of about 21 and others, have sought after the per cent, of oxygen, the remainder cause of this extraordinary pheno- being azote, or nitrogen,-about menon, and have contributed to one per cent., in the driest weather, explain it.” But though this par- of aqueous vapour, and about the ticular fact is so extraordinary, it thousandth part of the whole being falls so little under the notice of carbonic acid gas. All other aerial ordinary men, that they, judging mixtures and gases are in a shorter by their sensations, imagine their or longer time destructive of life. bodies vary in temperature like Some cannot be respired at all; the things around them. At the others again can be respired for a same time, there is no person so short time, but life cannot be long unobserving or so uninformed as sustained by breathing any air but not to know that animals possess the mixture which constitutes the a power of generating and creating atmosphere. The first well aseerheat. It is this power which pre- tained fact is, that all animals in serves the temperature of the body breathing the atmosphere vitiate at the same point, when other ob- the air; a portion of oxygen disjects are much colder. In fact, appears, and a portion of carbonic though the production of animal acid gas is formed. They take oxheat is known to every man, it is ygen gas into the lungs, or some so extremely familiar, he having corresponding organ, and give out felt it long before he had a capacity carbonic acid gas. This fact is infor making remarks, it having variably accompanied by another, glowed in his cheek with his first namely, that the blood, entering exertion, and been felt at his first the lungs by the pulmonary artery, blush, that very few persons ever changes its colour from dark purthink of inquiring into its cause. ple to bright red, loses the properIt has been said, that a man is fit ties of venous, and becomes artefor a metaphysician when he once rial blood. There cannot be any doubts the existence of matter; doubt that this change in the blood and a man seems, in like manner, is the consequence of inhaling fit for an inquirer, who asks himself oxygen gas and exhaling carbonic how the heat is produced which acid gas. As carbonic acid gas never allows him, during life, contains its own volume of oxygen though exposed to the greatest de gas, and as the quantity expired is gree of cold, to sink down to the in general nearly e equal to the temperature of ice. The fact is so quantity of oxygen which disapfamiliar, that every man supposes he can explain it, till he makes the attempt; and then he finds, indeed, great difficulties. Ever since the time of Lavoisier, the effect of re pears, it has been supposed, and this is the theory most generally adopted at present, that the oxygen inhaled goes immediately to convert the carbon of the venous blood into carbonic acid gas, and that consequently no oxygen gas is absorbed by the blood. Dr. Edwards, however, has lately shown, from a variety of experiments, described in his work, "De l'Influences des Agens Physiques sur la rie," that the carbonic acid gas expired does not always equal the quantity of oxygen inspired; and he has, moreover, shown, by making animals breathe, for a short time, air in which there is no oxygen, that they even then expire carbonic acid gas; whence he concludes that the oxygen inspired is absorbed by the blood, which at the same time gives out carbonic acid gas. This fluid, he supposes, exists in the blood, ready formed; and in support of this view, he mentions the circumstance of carbonic acid gas having been found in the mass of the blood. Between these two explanations, we must leave the reader to decide for himself, remarking, that at present the latter appears to us the more probable, but requires to be confirmed by further experiments. Whichever of the explanations, however, may be adopted, the great fact is still the same, the oxygen of the atmosphere is taken into the lungs, and a quantity of carbonic acid gas, about equal, on ordinary occasions, to the oxygen which disappears, is - given out. A common sized man consumes about 46,000 cubic inches of oxygen per day, and makes about twenty respirations in a minute: but these circumstances vary in different individuals. It has also been found, that several circumstances influence the production of the carbonic acid gas in the same individual. Thus it is diminished by taking intoxicating liquors, 0 living on vegetable diet, and by using large quantities of mercury 2 or nitric acid. 9 As edt in general no alteration takes place in the quantity of azote contained in a specific quantity of atmospheric air which has been breathed by animals, it has been in general concluded ed that it was not absorbed, and there have been many doubts as to the use of this 3 large quantity of azote. It is, however, quite clear that it is inhaled, or taken into the lungs, as well as the oxygen with which it is mixed; and some late experiments of the gentleman we have just mentioned, as well as some previously made by Messrs. Allen and Pepys, make it probable that it is absorbed; the quantity absorbed and the quantity exhaled being, in ordinary occasions, about equal. Admitting this, it does not still explain the use of azote in the atmosphere; and we want to know what change it undergoes, if any, and what is the use of absorbing and giving out equal quantities of this fluid. The particular experiments which seem to decide the question, was making animals breathe air in which there was little or no azote, its place being supplied by hydrogen, when it was found that hydrogen was absorbed and azote exhaled. M. Despretz, however, whose name we have already mentioned, denies the absorption of azote, though he admits its constant exhalation, and mentions the experiments of Magendie, which show that the azote is derived from the food, and that animals cannot subsist on food wholly destitute of azote. About this part of respiration, then, there is a doubt; and it remains for future discoverers to decide how and for what purposes all this quantity of azote is employed. The probabilities are in favour of the absorption, and its gradual conversion into the constituent parts of the body; but in this supposition, how the exhaled azote is produced, must still be accounted for. The alternate inhalation into, and exhalation of air from the lungs, with the changes described, constitute the function of respiration. The question now occurs, How does this process generate heat? "It is known that the habitual temperature of an animal is high in proportion as his respiration is active; but how does inhaling and expiring air preserve the body at about an equality of temperature, and carry that heat to the farthest |