280 Assimilation and Elimination of Nitrogen by Plants and Animals. {CHEMICAL NEWS, June 13, 1863. a perfectly anhydrous compound ether, tested as above. | porting cattle, and not exporting any other provisions, It is then heated for twenty or thirty hours at about cannot be maintained in its normal condition without an 150°. If the alcohol is anhydrous the mixture should importation of manures from extraneous sources, unless not become acid. indeed the culture of forage crops abstracted from the atmosphere the nitrogen that the cattle continually transferred to it. 6. The presence of a small quantity of alcohol in a neutral and anhydrous ether, acetic ether for instance, may be detected by heating the ether with a known weight of quite pure acetic acid. The standard of the acid will diminish according to the amount of alcohol. Comptes-Rendus, lvi., No. 18. TECHNICAL CHEMISTRY. With the known constant composition of the atmosphere, it appears, therefore, that there must be some mode in which the large quantity of nitrogen eliminated by animals is compensated, and which has the effect of abstracting from the atmosphere four or five kilogr. per hectare annually, taking the live weight of animals fed by a hectare at 100 kilogr. There appears to be no evidence of the direct Assimilation and Elimination of Nitrogen by Plants and assimilation of nitrogen by plants. All the ex Animals. MM. DUMAS and Boussingault have represented the general features of the balance existing between the phenomena of animal and vegetal life, but many questions of detail still remain to be determined, and one of the most important is that relating to the restoration of nitrogen to the atmosphere by animals, its passage from the atmosphere to plants, and thence again to animals. The experiments of MM. Edwards, Dulong, Despretz, Regrault, and Reiset have shown that animals eliminate nitrogen. The amount of nitrogen thus liberated is not more than about 1 per cent. of the carbonic acid expired, and it varies according to the feeding and condition of the animals. In agriculture it has been considered that all the nitrogen of the food of animals, over and above that assimilated by them, is restored to the land in the form of manure. But this is not the case. When the study of this subject was undertaken, in 1847, by M. Barral, only two experiments had been made with regard to it by M. Boussingault. He found that during twenty-four hours a horse eliminated twentyfour grammes of nitrogen, and a milch cow twentyseven grammes; in the one case 17 per cent., and in the other 13 per cent. of the nitrogen in the food. M. Barral has since found that, in the twenty-four hours, an adult man eliminates from nine to fourteen grammes of nitrogen, an adult woman about twelve grammes, and a child five years old three grammes, corresponding to more than a third of the nitrogen in the food. A sheep in the same time eliminates about six grammes, one-third or one-fourth the nitrogen in the food. Very nearly the same results have recently been obtained by M. Reiset with fattening cattle. The general result of the observations was, that in the twenty-four hours, forty eight grammes of nitrogen were required in the food for each 100 kilogrammes of live weight, and that one-fourth of this was eliminated and returned to the atmosphere as nitrogen. In a year, the same live weight would eliminate 4380 grammes of nitrogen. In other words, a consumption of food equivalent to 6000 kilogrammes of hay involves a loss of 1500 kilogr. This result confirms M. Boussin gault's opinion that farm animals are not, as is supposed, producers of manure, but rather consumers of manure; they convert fodder into materials rapidly assimilable by plants, only at the cost of a considerable loss. It appears from this that the practice of green manuring is advantageous when it is not necessary to obtain manures more rapidly assimilable, or when the feeding of cattle is not remunerative. It also follows that the fertility of a farm supComptes-Renduɛ, lvi., 765. periments that have been made on this subject have observations show that plants obtain a part of their given negative results. Still, M. Boussingault's nitrogen from some source other than the soil or the manure supplied to them. They obtain that nitrogen indirectly from the atmosphere. With the view of elucidating this subject, M. Barral, in 1851, commenced observations of the rain-water falling in the neighbourhood of Paris. He found nitrate of ammonia to be constant in the atmosphere, and that rain-water always contains sensible quantities of nitric acid and ammonia. But the quantity was insufficient to account altogether for the elimination of nitrogen by animals, though it was sufficient partly to account for the production of crops from unmanured land under the bare fallow system. The Function of Atmospheric Oxygen in the Destruction of Animal and Vegetal Substances after Death, by M. PASTEUR.* THE most ordinary observation has at all times demonstrated that animal and vegetal substances, exposed after death to contact with atmospheric air, or buried in the earth, disappear, in consequence of various transformations. Fermentation, putrefaction, and slow combustion, are the three phenomena which concur in the accomplishment of this great fact of the destruction of organic substances a condition necessary for the maintenance of life on the earth. Dead substances that ferment or putrefy do not yield solely to forces of a purely physical or chemical nature. It will be necessary to banish from science the whole of that collection of preconceived opinions which consist in assuming that a certain class of organic substances-the nitrogenous plastic substances-may acquire, by the hypothetical influence of direct oxidation, an occult power, characterised by an internal agitation, communi*Comptes-Rendus, lvi., 734, CHEMICAL NEW June 13, 1863. The Function of Atmospheric Oxygen. cable to organic substances supposed to have little stability. In M. Pasteur's memoirs, and more especially in a recent communication, he has pointed out precisely what are, in his opinion, the true causes of fermentation, and has stated the principal result of his researches on putrefaction, properly so-called. In every case, life, manifesting itself in the lowest forms of organization, appears to be one of the essential conditions of these phenomena, but life of a nature unknown hitherto; that is to say, without consumption of air or of free oxygen. He now endeavours to demonstrate experimentally that the slow combustion which takes place in dead organic substances, when they are exposed to the air has, in most cases, an equally intimate connection with the presence of the lowest forms of life. This leads to the general conclusion that life takes part in the work of death in all its phases, and that the three terms of that perpetual return to the atmosphere, and to the mineral kingdom, of the elements which vegetals and animals have abstracted from them, are correlative acts of development and of the multiplication of organised beings. In May, 1860, an exhausted flask, of 250 cubic centimetres capacity, containing 80 cubic centimetres of sugar solution with yeast, which had been heated to ebullition, was filled with air. Immediately after admitting the air, the point of the flask was again sealed by the blowpipe. Under these circumstances, it often happens that the liquid in the flask does not give rise to the production of infusoria or micoderms, and that it remains limpid after the admission of air to the flask. This was the case in the above-mentioned experiment. The liquid was still unaltered in appearance on February 5, 1863, and at that time the air in the flask was found to consist ofOxygen Carbonic acid Nitrogen by difference 18.1 This shows that, during the lapse of three years, the albuminous substances of the yeast water, associated with sugar, and exposed to ordinary atmospheric air under conditions in which animalcules or micoderms were not developed, had absorbed 2.7 per cent. of oxygen, which they had partially converted into carbonic acid. This direct oxidation or slow combustion was very slight, although the flask had been kept for eighteen months at a temperature of 25° to 30°. C. On March 22, 1860, a flask of 250 cubic centimetres capacity, and containing 60 to 80 cubic centimetres of boiled urine, was filled with air deprived of organised germs by heating it. The liquid was still quite limpid in January, 1863. Its colour had become slightly darker. A crystalline sandy deposit of uric acid had separated in small quantity on the sides of the flask. There were also a few bunches of acicular crystals of lime phosphate. The urine was still acid, but not quite so much so as at first. It smelt exactly the same as fresh boiled urine. The air in the flask consisted of 281 On June 17, 1860, a flask of 250 cubic centimetres capacity, containing 60 cubic centimetres of milk, boiled two or three minutes, was filled with air that had been exposed to a red heat. On February 8, 1863, the milk was almost neutral to test paper, with a tendency to alkalinity. It had the ordinary taste of milk, with a slight flavour of suet. By standing, the fatty substance separated in clots, and by shaking the appearance of fresh milk was again presented; it was not at all curdled. The air in the flask consisted of The fatty substance of the milk had absorbed a large proportion of the oxygen, as in De Saussure's experiments with oil. But still, after three years, there remained some free oxygen, although the direct oxidation of fatty substances is considered to take place very readily. By repeating these experiments under the same conditions, but under the influence of the development of organised germs of the lowest forms of animal and vegetal life, all the oxygen of the air in the flasks was absorbed within the space of a few days, with simultaneous disengagement of carbonic acid in varying proportions. On February 26 last, a flask containing 10 grammes of oak sawdust, and some water that had been boiled with it, was filled with air that had been exposed to a red heat. A month afterwards the air in the flask consisted of— Oxygen Carbonic acid. Nitrogen by difference In a similar experiment, made without any precaution for excluding organised germs, the air of a flask containing four litres was found, after fourteen days, to contain 72 per cent. of carbonic acid, and 300 cubic centimetres of oxygen had been consumed, while in the former experiment only a few cubic centimetres were consumed. This ready combustion of sawdust when exposed to atmospheric air was long since observed by De Saussure in his researches on the formation of soils. Whence arises this great difference between the results of the two experiments? At first sight there appears to be no clue to it. But if the surface of the sawdust is examined by the microscope, it is found, in the case where no precaution was taken to exclude organised germs, to be covered with a scarcely perceptible film of sporules and mycelium of various micoderms. In examining the slow combustion of dead organic substances under the influence of atmospheric oxygen alone, it will be found that it varies in degree and in mode of action, according to the nature of the substances, almost as the oxidation of metals differs. But the important fact is, that though this slow combustion takes place independently, it is scarcely sensible in air that is deprived of the germs of inferior organisms. This oxidation is disproportionately greater and more rapid when organic substances are in contact with mycoderms, &c. These minute beings are agents of combustion, whose energy, differing according to their specific nature, is sometimes extraordinary, as, for All the oxygen that had been absorbed had been con- instance, in the oxidation of alcohol, acetic acid, sugar. verted into carbonic acid. The constituents of living organisms might be regarded as being comparatively indestructible, if it were not for these minute beings, which are apparently without any use. Life would become impossible without them, for the restoration of that which has ceased to live, to the atmosphere and to the mineral kingdom, would be suddenly suspended. The above experiments by themselves might be open to a serious objection. The organic substances were not only dead, but were always heated beforehand to the temperature of boiling water, and it cannot be doubted that they undergo change at that temperature. It was necessary therefore to examine the slow combustion of organic substances that have not been so heated. M. Pasteur has succeeded in exposing to air, free from organised germs, fresh liquids that are in a high degree susceptible of putrefaction, such as blood and urine. Some flasks containing pure air and blood taken from a dog were deposited with the Académie last March, and after having been exposed, since then, to a temperature of 30° C., it had not undergone any kind of putrefactive change, and its smell was quite fresh. By analysis of the air in flasks containing blood, and kept for a month or six weeks at a temperature of 30°, there is but a slight absorption of oxygen recognisable, amounting to 2 or 3 per cent. Urine enclosed in flasks in the same manner, remained perfectly fresh. After forty days the air in the flask consisted of The conclusion to which M.. Pasteur has been led by these observations, is therefore the same as in the case of organic substances that have been heated, and they serve to complete the evidence he has, during the last few years, brought forward to show that the doctrines of spontaneous generation and the modern theory of fermentation are no longer tenable. On Destructive Distillation, considered in Reference to Modern Industrial Arts,* by B. H. PAUL, Ph.D. THE effects produced by the application of heat to various substances must have been among the earliest pbserved chemical phenomena. The differences existing between the effects produced by heat upon different substances were recognised at a very remote period in the history of chemistry, and among them the phenomena of distillation received especial attention. In some cases the application of heat to a substance has the effect of dissipating it entirely; such substances, of which water is a familiar example, are said to be volatile, and if substances of this kind are heated in closed vessels of suitable construction they may be recovered again, in their original condition, by the condensation of their vapour. This, in the strictest sense of the term, constitutes distillation. The volatile substance, absorbing the heat applied to it, becomes converted into vapour;-by abstracting from that vapour the heat which has been absorbed, it is converted into the original substance. In distillation is employed as a means of separating volatile substances from others which are not volatile, and which are, in contradistinction, termed fixed substances. This distinction between fixed and volatile substances is, however, in most cases merely relative, and it applies only to such a range of temperature as is com* Read before the Societ of Arts, May 27, 1863. this way CHEMICAL NEWS, June 13, 1863. monly attainable. There are good reasons for the opinion that the substances commonly regarded as fixed, might be converted into vapour if their temperature could be increased to a sufficient degree. But among the substances which, in this limited sense, are termed fixed, there are some which certainly cannot be converted into vapour, in any case, without entirely losing their identity; without, in other words, being converted into totally different substances. Thus, for instance, wood is not a volatile substance, and at the same time it is not a fixed substance, except within a certain limited range of temperature. When heated much above the boiling point of water, wood is partially converted into vapour, to an extent proportionate to the temperature employed, but the vapour so produced cannot be reconverted into wood by cooling it, as the vapour of water can be reconverted into water. The change produced by the heating is a true chemical change. Most substances analogous to wood undergo a change of this nature when heated in close vessels; they are, in chemical language, decomposed, and the substances into which they are converted are called the products of the_decomposition. These products are partly volatile. It is only in this way that substances which are not in themselves volatile can be said to distil, and it is this conversion of substances, by the application of heat, into new substances, that constitutes what is termed destructive distillation. The products of this alteration present, in all cases, a general similarity. There is, in the first place, the carbonaceous residue, which cannot be volatilised—the "coal," as it was formerly called. Amongst the volatile products, water and oil are conspicuous; there are generally some substances dissolved in the water, communicating to it peculiar characters, according to the nature of the material distilled, and in all instances some gas is produced. In the earlier days of chemistry the destructive distillation of organic substances was considered to effect a separation of their component parts; it was looked upon as a means of analysing both vegetable and animal substances. But it was found that the products of the destructive distillation of a substance varied in amount according to the heat applied to it, and, consequently, when quantitative relations became an important consideration in chemistry, this opinion was abandoned, and it has long since been generally admitted that the alteration such substances undergo in destructive distillation is greater than a mere separation of pre-existing components,-that it consists in an entire destruction of the original substance, with simultaneous production of new substances. consists in a disturbance of the chemical equilibrium This decomposition of an organic substance by heat upon which its existence depends; the products to which it gives rise are substances capable of existing at the higher temperature. All organic substances are characterised by their liability to decomposition by heat, but they differ among each other very much in their capability of supporting heat, or, in other words, in their liability to decomposition under its influence. For every organic substance there is a particular range of temperature within which its existence is possible, and beyond the higher limit of which it undergoes decomposition. Hence there is an intimate and essential connexion between the nature of the products and the temperature of the decomposition, and it follows that the special nature of the products obtainable in destructive distillation differs, according to the temperature at which it is conducted, no less than according to the material from 283 on the Continent. At Liege, for instance, coal was The distillation of coal at these works was conducted in a kind of close oven, or muffle, heated externally by furnaces. "The fire was got up gradually, until the oven became slightly red-hot, and it was then kept at that degree.. The heat being gradually communicated to the coal within the oven, first of all expelled its bituminous portion, which distilled off through a pipe, and fell into a receiver; when the coal had given off its bitumen it commenced to become slightly red-hot. "The oil and bitumen obtained in this operation almost paid the cost of it.. The pure bitumen was very thick and greasy, and equal to the best carriage grease. The oil did not differ from that obtained by distilling petroleum, except in being much less readily inflammable than the latter, and it could be advantageously employed in lamps by the country people. Nothing else was used for burning in the mines at Sultzbach." Prior to the time when Lavoisier wrote on this subject, the product of destructive distillation to which-with some few exceptions which I shall afterwards notice most attention was directed, was the oily product. The characters of the oil obtained by this means from different substances are often described in old chemical works. Sometimes it was called tar, that term being applied to those kinds of pyro-oils which were resinous and dried up by exposure to air, as in the case of that obtained from pine-wood, and which at the present time is still commonly known as tar. Some of these pyro-oils figure as medicinal agents in the pharmacopoeia of 1678, and amongst others the oil of coal-which is described as a fossil bitumen, bearing the names of carbo petræ, lithanthrax, sea-coal, or Newcastle coal-and the direction given is that "you may distil it as amber, so shall you have a spirit and oil." But this oil of coals soon became a matter of more extended observation, in consequence of the attempts made to use pit coal as fuel in smelting. For a long time these attempts were unsuccessful. At length, however, a method was found of removing the disadvantages of coal for smelting purposes. That method, as every one knows, was coking. The discovery of this method has been ascribed to Becher, who was in England about the year 1665, but he says himself that it was a German, of the name of Blavesten, who first suggested the idea of employing what he called "stone charcoal" for smelting iron. In any case the MM. Macquer and Montigny, in reporting to the oily product obtained from the coal, by heating it in close Académie on this manufacture, speak highly of its vessels, attracted the attention of Becher, and he put utility, and when we consider the extent to which the forward a project for making tar from coal, apparently in manufacture of which this was the first germ, has now conjunction with the production of coke, which is very grown, it appears that their opinion was well founded. often referred to in old works, but always in very vague The next person who made a step in this branch of terms, and nothing much seems to have come of it. manufacture was Lord Dundonald. The preparation of coke appears to have been still the predominating idea, but it was also thought that the volatile substances given off in this operation might be turned to account, as well as the coke. All the previous methods of obtaining these products consisted in distilling coal in close vessels heated externally, but Lord Dundonald's method consisted in partially burning the coal in a large chamber capable of being entirely closed, and admitting a regulated supply of air, just sufficient for maintaining the combustion of coal at the desired degree. The volatile products from the coal passed away through a pipe to a condenser, where they were collected. An account of the works erected on this plan at upper Cranston, is given in Sir John Sinclair's "Statistical Account of Scotland." The product obtained, besides coke, was a mixture of tar and water. This first product was submitted to distillation, yielding an oil lighter than water, and a solution of ammonia. This tar was sold for greasing cart wheels, at the rate of sixpence per Scotch pint. When the distillation was continued for four and a-half days, the residue, remaining in the still, was the tar suitable for coating ships, which was regarded as one of the most important of the products. When the distillation was continued for five and a-half days, the residue in the still was more pitchy; and after six and a-half days it was quite brittle. (To be continued.) The German chemist Neumann examined the oily products of the distillation of coal, and described them in his works as consisting of a "thin fluid oil" and another "thick pitchy oil." He obtained these by distilling the coal of Halle "with a fire gradually increased," and he states that "the coal, during the distillation, looked like melted pitch." Still these products were not turned to any useful purpose. However, the coking of coal, or the desulphurising, as it was sometimes called, became an important operation, and great interest was excited by it on the Continent. In 1765, the French Government thought it desirable to send a commission to this country, for the purpose of learning the art of coking. An account of their observations is given by M. Jars, the brother of one of the commissioners. He says:-"The English were the first to attempt rendering coal available for smelting purposes; the first trials are of a very remote date. And, among others, Swedenborg speaks of it as an art which in his time was not fully developed. But the industry of the English overcame all difficulties, and they succeeded, by means of very simple operations, in attaining the desired end, that is to say, in depriving pit-coal of the defects which render it unfit for smelting." The attempt to turn to account the volatile oily products obtained in coking coal was still continued, both in this country and 284 Holmes's Magneto-Electric Light. Holmes's Magneto-Electric Light. ON a former occasion we traced the history of the mode (CHEMICAL NEWS, June 13, 1863. magnets in position. The speed of the engine was not allowed by the Trinity House authorities to exceed 100 revolutions per minute, and other conditions were imposed, particularly with reference to the machine being driven by a direct-acting steam-engine without the intervention of a strap or band. It was necessary also to moderate the intensity of the electric current, so that the " shock" should be trifling, and not such as to affect the health of the attendants, who might occasionally, when on duty, place themselves in circuit. In ordinary cases the machine, with its boiler and steam-engine, would be placed in a building adjacent to the lighthouse, the wires being led thence to the lantern. At South Foreland, where two lighthouses on the mainland are situate within a thousand yards' distance, one machine-room, built in an intermediate position, and as nearly as possible half-way between the two, will suffice. It is always advisable to keep the engine away from the lighthouse itself, as a guarantee against the condensation of steam upon the glass reflectors and window panes. With respect to the lamp and optical portion of the apparatus, it will be sufficient to describe the arrangements for a fixed light at Dungeness. Two regulators or lamps are employed for each lens, and these lamps are arranged on two travelling platforms in such a manner that a mere touch is sufficient to withdraw one and to slide another into its place. The manner of working in the lantern is this:-At starting, all the lamps are charged with carbons, two lamps being in their respective lenses, the others standing on their corresponding platforms behind, ready to replace those now in focus. At sunset the machine is started, and the attendant has merely to draw two bolts in either of the lamps in focus, and the light is instantly showing with its full intensity. This lamp does not require any attention for about three hours and a-half, if the carbons are well paired for hardness; but if these differ much, then the luminous point will gradually rise or fall above or below the focal plane, and will require occasional adjustment. After a few months' practice, ordinary light-keepers are able to pick. out pairs of carbons that will retain their position in the focal plane during the whole time of their consumption. The machine is put in motion by a direct-acting At about three hours and a-half from the time of lightsteam-engine, and by means of a crank fixed on the ending, the carbons will require changing. This is effected of the axle opposite to that upon which the commutators are mounted. The manner in which the electricity is generated and evolved may be described thus :-At every revolution of the wheels the entire series of cores and helices on each wheel passes between the poles of its two rings of magnets, and consequently at every revolution about 85 lbs. of soft iron are magnetised N-S, and again changed to S-N, forty-four times; and, as the machine makes 110 revolutions per minute, these changes in the magnetic state of the soft iron cores, or armatures, take place 4840 times in a minute. In order to obtain the maximum of power from the machine, two points had to be specially attended to in its construction: first, that the magnets should retain their force for a lengthened period without sensible diminution; and secondly, that during their revolution the ends of the cores should pass as closely as possible, without actually touching, the poles of the magnet. By neglect of this latter precaution, a large machine, in which wood was employed in the mounting of the magnets, met with total destruction whilst under trial at Brussels, in consequence of the humidity of the atmosphere disarranging the adjustments; this casualty is now rendered impossible, by the use of a framework of brass, and of strong set-screws for fixing the * Vide CHEMICAL NEWS, vol. vii., p. 247. without extinguishing the light, as follows:-The attendant pushes in the two bolts which he withdrew at lighting, which stops the action of that lamp, but does not immediately extinguish it; he then passes to the lamp in focus at the other lens. On drawing the bolts of this lamp, the current is diverted, and this lamp now lighted. The first is now withdrawn, and the lamp standing on the platform behind it is pushed forward in its place; and when the used lamp is cool, the attendant mounts in it a fresh pair of carbons, and places it ready to be used again in its turn. Thus, while the speed of the machine is maintained and the lamps changed as directed, the light may be continuously exhibited any number of hours or days. The internal construction of the lamp itself is not very different from those already known and used in this country. The carbons are mounted upon sliding brackets, the interval between them being regulated and main tained by the action of an electro magnet. There are three or four screws or studs provided at the back of the lamp for altering the adjustments, and starting or stopping its action. The communication with the main wires the instrument rests when in position. The magnetois effected by means of a pair of metallic rails upon which electric apparatus is equally applicable to revolving |