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Miscellaneous Answers to Correspondents.

stance is quickly transformed, with evolution of ammonia, into a dark-coloured tenacious mass, which is dissolved in acetic acid and diluted with alcohol for the preparation of a dye of convenient strength.

The French mode of proceeding appears to differ from the foregoing by requiring the addition of aniline or toluidine to the magenta compound.

CORRESPONDENCE.

A Simple Self-Adjusting Barometer.

To the Editor of the CHEMICAL NEWS. SIR,-The less complex a barometer is, generally speaking, the greater may be the reliance on its indications; and, if self-adjusting, and not liable to error of any kind (save that from heat), nor subject to derangement (and if accidentally deranged easily repaired), and if perfectly portable so much the better. While thinking over these and other the essentials of a perfect instrument, the following adaptation of the siphon barometer occurred to me, which, if the idea be of any value, your readers are wel

come to:

The requisite tube is the ordinary siphon, with the shorter limb pressed as near to the longer one as the process of filling with mercury will allow. On the surface of the mercury in the shorter limb is to be placed a float made of some light substance, to which a silk string, which passes over a pulley placed a few inches higher than the top of the longer limb is to be attached. The height of this pulley, as well as the length of the shorter limb, will depend on the intended use of the instrument. A light graduated scale is to be attached to the string opposite the level of the mercury in the longer column, which, together with the float, should be nicely balanced by a weight on the opposite side of the pulley. By this simple contrivance the scale will rise and fall along with the mercury beneath the float, and thus will indicate double its own (which will be the true) rise and fall of the mercurial column.

By placing a cistern on the shorter limb, the play of the scale would of course be greatly diminished, but it would render the instrument more unwieldy, and doubly or more expensive.

Neither of the above instruments would be very portable without a stop-cock; but the addition of one to the former would be an improvement, inasmuch as the limbs could be brought nearer together, and thus the scale would be brought into close proximity to the mercurial

column.

By using a stop-cock two straight tubes would be required, which would have to be joined by it at the bottom, and thus, by turning the tap and corking the open end of the shorter tube, all egress of mercury or ingress of air would be stopped.

The best form of junction-pipe or stop-cock will suggest itself to any one capable of constructing a barometer; but one thing should be borne in mind, viz., that it will be almost, if not quite, impossible to fill the tube if no provision is made in the junction-pipe for that purpose. I am, &c.

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paint their faces, he analysed a bottle of it bearing a French and Arabian label, and was not a little surprised to find a solution of Hofmann's "acetate of rosaniline in rose water:

SCIENTIFIC SOCIETIES.

MEETINGS FOR THE ENSUING WEEK.
May 18. Monday.

BRITISH ARCHITECTS-9, Conduit Street. 8 p.m.
ASIATIC-5, New Burlington Street: 3 p.m. Anniversary.
19. Tuesday.
CiviL ENGINEERS-25, Great George Street, Westminster.
8 p.m.
STATISTICAL-12, St. James's Squate. 8 p.m.
PATHOLOGICAL-53, Berners Street, Oxford Street. 8 p.m.
ETHNOLOGICAL-4, St. Martin's Place. 4 p.m. Anniver-
PHARMACEUTICAL-17, Bloomsbury Square: 8 p.m. Con-
ROYAL INSTITUTION-Albemarle Street. 3 p.m. Professor
Tyndall," On Sound."

sary.

versazione.

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In publishing letters from our Correspondents we do not thereby adopt the views of the writers. Our intention to give both sides of a question will frequently oblige us to publish opinions with which we do not agree.

R. and Co.-The means to be adopted for deodorising hydrocarbon oils depend upon their nature, or rather upon the source from which they are obtained. What would be effectual in one case would not be so, perhaps, in another.

A Friend.-Our reporter most unaccountably neglected to attend the meeting of the Society. We will endeavour soon to obtain some information respecting it.

W. J. P.-1. It appears with tolerable regularity, and can be obtained

by subscribing through any foreign bookseller. 2. We do not know M. Violette's address. A foreign bookseller would probably procure a copy of the memoirs for you.

I

THE CHEMICAL NEWS.

VOL. VII. No. 181.-May 23, 1863.

CHEMISTRY OF AGRICULTURE. JUST sixteen years have elapsed since the sixth edition of Baron Liebig's work on the "Chemistry of Agriculture and Physiology" was published in Germany, and during that time much has been achieved in regard to this important subject both in observation, in thought, in the more just appreciation of long-known facts, in the interpretation of experimental results, and in a more critical examination of theories. During that time, great changes have taken place in various branches of the practice of agriculture. Not to speak of the application of steam in cultivation, the use of artificial manures has extended to a degree far exceeding the most sanguine anticipations that were formed when guano and soluble phosphates were first recommended to the attention of the farmer. The results of these changes are generally regarded as highly favourable, both in regard to the extent of land under cultivation, and as regards the produce obtained.

It has generally been supposed that, in this country at least, the recognition of scientific truth, as a safe guide in the practical operations of farming, has been the means of effecting very important improvements, and that the principle embodied in the motto of the Royal Agricultural Society" Practice with Science "had become, directly or indirectly, the general and leading principle of the prosecution of this art.

The prominent part that Baron Liebig has taken in contributing to this modern development of agriculture is too well known to need any minute account of the service he has rendered in suggesting and stimulating inquiry in this direction. This circumstance, together with the fact that he has continued to devote considerable attention to the chemistry of agriculture, will alone be sufficient to excite great interest in the new edition of his work that has just appeared. This edition contains, besides the original work, a new volume devoted to the elucidation of the "Principles of Agriculture," and an introductory essay that is not the least interesting portion of it.

In this introductory essay, Baron Liebig expresses an opinion widely at variance with that above mentioned as generally entertained, and he appears to regard the present condition of agriculture as being more retrogressive than progressive. It is true that he treats of agriculture generally, as practised in Germany as well as in other countries, but on the whole this view of the state of agriculture which he puts forward has also especial reference to this country.

In the preface to this new edition he says, that, since the publication of the last edition, he has had ample opportunities of becoming acquainted with the obstacles which prevent the diffusion of scientific doctrines in the sphere of practical agriculture. He refers these obstacles chiefly to the absence of any communion between practice and science. Agriculturists, he says, are very

generally impressed with the prejudices that a degree of education inferior to that required in other arts is sufficient for the practice of their art; that the practical capability of the farmer is injured by a habit of reflection, and by the adoption or consideration of the results of scientific inquiry; that whatever involves the exercise of thought is designated by him as theoretical, and, as the direct antithesis of practice, is either little valued or disregarded.

There are many who will regard this as a remarkable statement, so far, at least, as it is intended to apply to this country, where it has been believed that the characteristic feature of our modern agriculture was an eager acceptance of the aids of science, and the expression of a demand for that aid even greater than science was able to gratify. Baron Liebig, however, admits it to be the fact, that the attempt to apply theory or scientific doctrines in agriculture has frequently been attended with disadvantage, that the means adopted by the farmer with the view of improvement, have often turned out failures; but he does not allow such unfavourable results to be any sufficient reason for a disinclination on the part of the farmer to depart from long-established custom. He throws the blame of these results upon him because he did not know in what way to apply scientific doctrines rightly. But this censure is unjust. If it be the business of the farmer to know the use of scientific doctrine, and to learn the art of applying it to his purposes, it is not the less the business of the chemist to teach him that knowledge and that art; to furnish him, in an available form, with those results of science which are capable of being applied usefully. It cannot be expected that the farmer will consider critically the value of the suggestions of the chemist before he has put them in practice. It is only by the result of their adoption that he is capable of judging, and if, following the guidance of the chemist, he finds that the promised advantage is not realised, it is quite natural that he should form an unfavourable opinion of the proposed innovations, and become confirmed in that tendency to adhere to customary routine which is a universal, and not an irrational, characteristic of agricultural practice.

The customary routine of agricultural operations, however defective they may be in particular cases, has become established by the exercise of precisely those mental functions which are employed in scientific research —observation and experience; and though, in agriculture, their exercise is limited by the practical object in view, there can be no doubt that, in reality, agricultural customs represent natural facts to a greater extent than even science is competent to explain. It is no reproach, therefore, to the farmer if he adheres to a system that he knows by experience to have brought him certain results, or that he refuses to adopt another system until he has sufficient evidence that its results are more advantageous than those with which he is familiar.

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Absorption of Gases by Charcoal.

This natural conservative tendency has been strengthened by the failures resulting from premature application of scientific doctrines to agricultural practice. This is really the reason why farmers are in many cases averse to the adoption of improvements suggested by science. It is not because they are "destitute of all understanding," as Baron Liebig asserts, or because they pretend to deny the existence of any connexion between scientific doctrines and the phenomena presented by agriculture, but because it is still questionable whether those doctrines are correct, and consequently whether they really furnish the means of improvement. That is the reason why they select to be guided by tradition and received opinion rather than by the untried precepts of science. The science that is to be of value in agriculture, and whose value will be recognised by farmers, must grow out of the practice of the art, and not be a mere speculative grafting upon it. The accumulated data of ordinary experience must furnish the basis for its construction, and its doctrines must rest on evidence of reality, and not of mere probability. It may be a slow growth, but it must be a sure one. If there be an established and invariable connection between the use of superphosphates and the production of a large root crop, between the use of ammoniacal manures and the increase of corn crops, these manures will continue to be used, and their use will constitute the scientific practice of agriculture, independent of the questions whether they be specific manures for those crops, or what becomes of that nitrogen which is applied as manure and does not reappear in the crop. These are abstract scientific questions of high interest for the chemist, and of probable importance to the future of agriculture, but it is by no means a logical conclusion that the undoubted fact that the use of ammonia as a manure has a remarkable influence upon the production of corn, greater than in practice appears to result from the use of any other manure, should be disregarded because the precise functions of ammonia are as yet but partially known; nor is it rational for this reason to denounce the application of that fact, to the extent to which present knowledge reaches, as a folly and an error.

In reference to the controversies that have been maintained of late years as to agricultural subjects, Baron Liebig maintains that practical men have not understood the conclusions of science, that the disputes have not been as to scientific principles, but as to the false conception of those principles. He complains that his views have been altogether misunderstood, and claims the right to "purify his doctrine from the dirt by which it has for so many years been sought to render it unrecognisable." But the justice of this complaint is more than doubtful. Few scientific men have enjoyed greater popularity, in reference to any subject, than Baron Liebig has, in this country, in connection with the chemistry of agriculture, or have had their views so widely propagated and so generally received, as those put forward by him some years ago. Chemists of distinction have vied with each other in the translation of his writings, and in the exposition of his views. Agriculturists have accepted them unconditionally, and with the fullest confidence. It is, indeed, difficult to imagine any more thorough recognition possible than was accorded in this country to Baron Liebig's views on agriculture. The number of his adherents is now undoubtedly very much smaller than it was, but that circumstance is less referable to misconception of his views than to an alteration of opinion with regard to them. If Baron Liebig's views have suffered in this country, it is

CHEMICAL NEWS, May 23, 1863.

rather in consequence of the eagerness with which they were accepted in the first instance, and the too great significance attached to them as first propounded, and while still too insufficiently founded upon fact. Whatever defects may have been found in those views do not arise from want of regard for, or of acquaintance with them.

The exhaustion of the soil is a subject on which Baron Liebig especially dwells. He denounces the modern systems of agriculture as "systems of plunder," and predicts the reduction of land to an irremediable state of sterility as a necessary consequence of their continuance. He regards it as a signal defect that farmers do not keep account-books, in which each of their fields are entered, and a debtor and creditor account kept of all that is removed from, and supplied to them in the shape of mineral constituents. He considers that many farmers are, in consequence of this defect, ignorant of what condition their fields are in. It may be added also that, if this plan were adopted, there would be as much difficulty in determining by its means when a field was in good or bad condition. For with the almost infinite diversity of soils, as regards their resources of manure constituents, it would be impossible to establish any standard by which to make the determination. Moreover, the chemical composition of a soil is far from being the only condition of fertility. Many other conditions, that are as yet but little understood, contribute more or less to the capability and value of soils, and there is much to be learnt with regard to these conditions before there can be any sufficient grounds for recommending a refinement of such a nature as keeping accounts of the mineral constituents of his soils, the utility of which is still doubtful.

SCIENTIFIC AND ANALYTICAL CHEMISTRY.

Absorption of Gases by Charcoal. DR. R. A. SMITH* has given the following as the results of his experiments on this subject:

Charcoal abstracts oxygen from atmospheric air at ordinary temperatures.

The absorption of oxygen continues for a long time, but the greater part takes place during the first part of the time the charcoal and air are in contact.

Hydrogen, nitrogen, or or carbonic acid are not absorbed at the same time as oxygen, from gaseous mixtures.

The amount of gas absorbed by charcoal is in some degree proportionate to the condensibility of the gas; but this is not the only determining circumstance, in the case of oxygen at least.

The separation of oxygen that is absorbed by charcoal cannot be effected without production of carbonic acid, even at 212° F., and more slowly at lower temperatures.

The absorptive power of charcoal differs for different kinds very much, so does the capability of combining with oxygen; animal charcoal excels wood charcoal, in this respect..

into an atmosphere of other gases with a force equal to Nitrogen and hydrogen absorbed by charcoal, diffuse a three-quarter inch column of mercury. Water expels mercury from the pores of charcoal instantaneously.

* Proceedings of the Royal Society, xii., 424.

CHEMICAL NEWS,

May 23, 1863.

Disassociation of Carbonic Acid.

Dr. Smith concludes from his observations :—

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That the selective character of porous bodies may be kept at a strong red heat for more than an hour. Its closely related to

1. The condensibility of gases;

2. Attraction, and perhaps tendency to combine;
3. Capacity of combination.

That in any case the attraction which determines the condensation of a gas is exercised at a distance greater than the distance of the atoms or molecules in combination.

That the gases in porous bodies lie in concentric strata, around the particles of the solid, which strata are unequally attracted according to their distance.

That chemical attraction cannot be distinguished from physical attraction, though attraction may exist without effecting its ultimate result of combination, and that the influence of mass upon chemical action may be due to this connection.

That there is no evidence of the existence of a specific attractive force determining chemical change, but only evidence of combination.

Mr. Hunter, of Queen's College, Belfast, has also published some results relating to this subject. He has adopted the method employed by De Saussure. The charcoal was heated to redness before each experiment, and, while incandescent, plunged into the dry gas confined by mercury. The absorption generally terminated at the end of twenty-four hours. The results obtained were as follows, for a temperature of oo C., and pressure of 760 mm:

TABLE II.

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power of charcoal, a piece of boxwood charcoal was absorption was then found to be 79, while in the ordinary way of heating it was 85. It would appear from these results that different kinds of charcoal differ in their absorptive power for different gases. Logwood charcoal absorbs most ammonia; fustic charcoal most carbonic acid; and ebony charcoal most cyanogen.

Disassociation of Carbonic Acid.

M. DEVILLE has continued his investigation of the phenomena of disassociation, for the decomposition of substances at temperatures below those at which they are permanently reduced to their elements. He regards the conversion of compound substances into a mixture of elementary substances, or more simple compounds, as being a change of state accompanied by all the circumstances which attend change of state effected solely by cohesion. Whenever heat is generated by combination, or when heat is absorbed by decomposition, the constancy of the temperatures at which the changes take place is a necessary feature of the phenomenon; it is the result of the sensible heat of combination or of the latent heat of decomposition. In combination, as in the condensation of vapour, heat is evolved; in decomposition, as in ebullition, heat is absorbed, and becomes insensible.†

Disassociation, or the decomposition of a substance, below the normal temperature of decomposition, is compared to the evaporation of a liquid below its boilingpoint, as being necessarily but partial, and dependent upon the temperature of the medium in which it takes place. By the term tension of disassociation is denoted the quantity of any substance decomposed in its own vapour, compared with the whole mass submitted to the action of heat.

In the same manner that water may be decomposed at a moderately elevated temperature, either under the influence of a solvent which abstracts one of its elements, or by means of mechanical action, so, likewise, can carbonic acid be decomposed, and more easily, in consequence of the slight tendency of carbonic oxide and oxygen to unite when disseminated through a large quantity of carbonic acid. The apparatus employed for this purpose consisted of an iron tube filled with fragments of porcelain, and passing through another tube of porcelain. The whole was heated to a temperature of about 1300° C., and a current of pure carbonic acid passed through it into a bath containing caustic potash, in which were immersed tubes filled with potash solution. The gas, which was sent through the tube at the rate of 7.83 litres per hour, was not entirely absorbed, and in the same time about 20 or 30 centimetres of an explosive gas was collected. The composition of this gas was constant, as follows :—

Oxygen Carbonic oxide Nitrogen

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Action of Nascent Hydrogen on Aldehydes.

This accounts for the presence of nitrogen in the products of disassociation.

This result, simple as it appears, does not admit of the tension of disassociation being calculated for the particular temperature at which it was obtained, even supposing that temperature to be known, for a portion of the disassociated gases may have recombined during the cooling.

M.

May 23, 1863.

of vapours was sufficiently copious, the temperature of the vessel was found to be raised to 394°5 C., notwithstanding the constant cooling effected by the mercury .vapour, which tended to reduce the sides of the vessel to the temperature of 350° C. It appears, therefore, that ammonium chloride does not undergo decomposition at 394°5, but that its constituents combine at that temperature with a disengagement of heat much more considerable in amount than the above numbers appear to indicate. By taking the density of the ammonium chloride vapour at 350° C. in mercury vapour, it was found to be roo instead of o'93, as indicated theoretically for eight volumes.

M. Deville then goes on to consider the very important phenomena recently observed by M. Pébal ‡ and Messrs. Wanklyn and Robinson,§ viz., the decomposition of ammonium chloride into hydrochloric acid gas and ammonia by the action of heat, and the decomposition of phosphorus perchloride and sulphuric acid. This experiment shows that it is advisable not to reject Deville considers that the conclusions which have been as inadmissible, the results of experiments because they drawn from these results are incorrect, and that they are not in accordance with atomic theories, which, howare analogous to the phenomena of diffusion observed by ever useful they may be as guides in new paths of Mr. Graham. Thus, for example, when potassium bisul-research, should, from the variations they have underphate or alum are submitted to diffusion, it is found that gone, be regarded as essentially ephemeral. these substances, whose existence at the ordinary temperature is unquestionable, cannot diffuse throughout an indefinite quantity of liquid without undergoing decomposition, by reason of the unequal diffusive capability of their constituents. It follows, therefore, that there is an actual exercise of force by which the constituents are separated, and which must not be overlooked in the explanation of the phenomena observed by Messrs. Pébal, Wanklyn, and Robinson. The same view is applicable to the diffusion of vapours whose constituents possess unequal capabilities of diffusion or transpiration. This agent of decomposition, observed by Mr. Graham, is so energetic that it is no longer possible to regard the decompositions effected by it as being spontaneous. That view does not afford any explanation of the fact that ammonium chloride, sulphuric acid, or phosphorus perchloride are susceptible of decomposition in their own vapour at the temperatures employed by the experimenters. The experiments of M. Marignac are much more decisive in their results as regards sulphuric acid; but they also show that the decomposition is very small in amount.

Referring to the application of the phenomena of disassociation by Cannizzaro and Kopp, with the view of showing that even the most complex vapours cannot represent eight volumes to an equivalent, M. Deville adds that the number of substances which may be so regarded is now so considerable that it would be inconsistent with the experimental results obtained by him and M. Troost to reject those facts on the pretext of considering those vapours which represent eight volumes as being decomposed at the moment of taking their density. Moreover, that argument would be dangerous when it serves only to support conjectural views as to the atomic constitution of chemical compounds. He has therefore thought it necessary to make an experiment with regard to this subject which would remove all doubts.

A vessel maintained at a constant temperature of 350° C. by means of mercury vapour was fitted with an air thermometer, which soon acquired a condition of equilibrium. By means of tubes connected with this vessel, two separate currents of hydrochloric acid gas and of ammonia were passed rapidly through it, and at an equal rate. At the moment the gases combined the air of the thermometer expanded suddenly, indicating a sudden elevation of temperature. By closing the leg of the thermometer at the moment when the disengagement Annalen der Chemie und Pharmacie, xlvii., 199.

§ Comptes-Kendus, lvi., 547.

Action of Nascent Hydrogen on Aldehydes. IT is known that MM. Wurtz and Friedel have converted several aldehydes into the corresponding alcohols by means of nascent hydrogen. They were unable to effect this change with the gas obtained by the ordinary methods of converting nitrobenzol into aniline, but they succeeded by using an amalgam of sodium.

It has occurred to M. Lorin* to effect this change by means of hydrogen obtained by the decomposition of water, at a moderately elevated temperature, by zinc in the presence of ammonia-the means by which M. Berthelot converted acetylene into ethylene. He has found that this may be done, that aldehyde and acetone are respectively converted into the corresponding alcohols, and that, in the case of aldehyde, this change is also accompanied by the production of ammoniacal compounds.

Dry aldehyde-ammonia was placed in contact with a water solution of ammonia and small fragments of zinc. The disengagement of hydrogen took place under slight pressure, and at a temperature of from 30° to 40° C.

After filtering the liquid, and distilling off one half, the distillate was saturated with dilute sulphuric acid, then again distilled from a water bath, and one-fourth collected. Carbonate of potash caused the separation of an inflammable liquid, decomposable by sulphuric acid with production of olefiant gas, and yielding with acetate of soda and sulphuric acid, acetic ether; in short, possessing all the characters of ordinary alcohol.

Acetone, carefully purified and treated in the free state in the same manner, gave rise to the production of propyl alcohol.

The quantities of the alcohols thus obtained did not amount by weight to more than one-fifth of the quantities that should have been obtained if the conversion had been complete. Accessory products were formed by the action of the nascent hydrogen, either on the aldehydes or on the alcohols.

In the experiment with aldehyde, the residue, saturated with potash and carefully distilled into hydrochloric acid, gave a crystalline deliquescent salt, soluble for the most part in absolute alcohol, and evolving an inflammable alkaline vapour when mixed with lime.

converted into aniline.
Nitrobenzol, treated in the same manner as above, was

* Comptes-Rendus, lvi., 845.

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