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smoke colour glass. The results exhibited were after an exposure of eight days, and showed that the parts of the board directly exposed to light were bleached; those protected by an opaque medium were not acted upon; while with the glasses of different colours intermediate effects were produced, those of the violet glass being most decided. Drying oils in conjunction with light rapidly bleach sulphide of lead, and boiled oil effects the bleaching still more rapidly. When water colour is used bleaching takes place, but much more slowly than in the case of oil. After quoting authorities, stating that generally light was advantageous to the preservation of pictures, Dr. Price showed a striking illustration of this fact. He had a picture painted, and then exposed it to the action of sulphuretted hydrogen, until it became sadly discoloured, and to all appearance destroyed. Some strips of paper were laid across the picture, so as to cover some parts. The picture, thus partially covered, was exposed to light for a long time. The result, as shown at the meeting, was very curious indeed, the parts of the picture exposed being perfectly restored, while those protected by the paper remained still discoloured. From his experiments he came to the conclusion that it was advantageous to have picture galleries well lighted, especially where, as in towns, the atmosphere was charged with sulphur compounds, and that it was quite a mistake to have curtains placed in front of pictures, with a view to their protection. In the course of his communication Dr. Price referred to the use of zinc paint for houses, and considered it likely to be acted upon, as the paint was rendered soluble by the acids contained in the atmosphere of towns.

Compounds of Copper and Phosphorus, by
Mr. F. A. ABEL.*

many advantages-especially as regards the tenacity, hardness, and homogeneous character of the metal produced. This he proposed to apply to the manufacture of tubes, sheathing, cylinders for calico printers, and manifold other purposes.

Since the date above mentioned, Mr. Parkes has obtained other patents for modifications and improvements in his original process, and the manufacture of phosphorised copper, containing from toper cent. of phosphorus, is now successfully carried on at the extensive works of the Stephenson Tube Company, in Birmingham, with which the patentee is connected.

This metal is forged, drawn, and rolled both hot and cold, and its successful application to the manufacture of tubes, cylinders, sheets, and various other purposes, has established its claim to the possession of those qualities which are stated by Mr. Parkes to be its especial characteristics-viz., great hardness, homogeneousness, smoothness and evenness of texture, and tenacity. Its employment for the manufacture of large cylinders for calico printing has been especially satisfactory, by reason of these qualities.

The successful issue of the whole manufacture appears, however, to depend upon the careful selection of materials, and upon certain niceties of manipulation, which are absolutely indispensable.

PHYSICAL SCIENCE.

Notes on the Fracture of Polished Glass Surfaces, by F. H. WENHAM.†

THE short communication which I submit to your notice scarcely merits consideration as a discovery; but as the microscope has in this case immediately detected the cause of a well-known phenomenon, I bring it forward as an example of the use of the instrument in practical investigations.

THIS paper was devoted to the description of a series of experiments made to ascertain if phosphorised copper It is a fact known to the philosophical instrument would be more effectual as a material for the manufac-makers that if a metal wire be drawn through a glass ture of cannon than the alloy now in general use. After tube, a few hours afterwards the tube will burst into referring to the different chemical compounds of copper fragments. The annealed glass tubes used for the water. and phosphorus known, Mr. Abel spoke of his experi-gauges of steam-boilers are sometimes destroyed in this ments on phosphorised copper, with respect to its tensile way, after the act of forcing a piece of cotton waste strength. He found that an ingot of copper one inch in through them with a wire for the purpose of cleaning area broke under a strain of about 25,000 lbs., that of a the bore. This will not happen if a piece of soft wood similar ingot of gun metal required 32,000 lbs. Whilst is employed. copper combined with 5 per cent. of phosphorus required 38,389 lbs., and with 14 per cent. of phosphorus the strain that the ingot would bear was upwards of 47,000 lbs. Although these experiments showed the very superior tenacity of the phosphorised copper, yet there were practical difficulties which prevented the application of this compound to gunnery. In the course of the discussion which followed the reading of this paper, Mr. Abel stated that this phosphorised copper would not be at all suitable for telegraphic purposes, as the presence of phosphorus was most detrimental to the metal as a conductor of electricity.

After the paper of which the above is an abstract had been read, Mr. A. W. Wills made the following state

ment:

So long ago as 1848 a patent was taken out by Mr. Alexander Parkes, of Birmingham, for the use of compounds of copper, zinc, nickel, and other metals, with phosphorus. The result of Mr. Parkes' experiments, more especially with respect to the copper compounds, had been so favourable as to enable him to claim for them

* Read at the meeting of the British Association.

The late Andrew Ross informed me that on one occasion, late in the evening, he lightly pushed a piece of cotton wool through a number of barometer-tubes with a piece of cane, for the purpose of clearing out any particles of dust. The next morning he found most of the tubes broken up into small fragments, the hard siliceous coating of the cane proving as destructive as he had previously known a wire to be.

After having drawn the point of a steel burnisher over the surface of a slip of polished glass, the following appearances will be observed under the microscope, using thirds object-glass. the polarising apparatus and selenite plate, with a twoA coloured stripe is visible in the passage of the burnisher, showing that the surface of the glass has been placed in a state of tension in the direction of the line. The glass, too, seems not altogether devoid of plasticity, for the waves of colour show that it has been carried forward in ripples, resembling the mark left on a leather-bound book after the passage of a blunt point. It may be inferred from this that the mere burnishing of the surface of the glass ↑ Read before the Microscopical Society.

42.

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with a substance inferior in hardness will, without any scratching, cause an irregular strain in the bore of tubes sufficient to split them, and the concussion attendant upon the fracture often reduces the tube to small fragments.

If the burnished lines upon the glass slip be examined a few days afterwards, the colours will have become much less visible, showing that the strained portions of the glass partly recovers its equilibrium.

On attempting to polish out a minute scratch on the surface of a piece of glass, it sometimes appears to widen during the process, and at length resolves itself into two irregular parallel rows. Also, a clean cut made with a diamond on a piece of plate-glass, if left for a time, the surface in the vicinity of the cut will break up, forming a coarse irregular line. If the diamond be raised and struck lightly on the surface of the glass, the form of the edges of the short stroke thus made may be plainly seen, using the binocular polariscope. A conical ridge of glass appears to be left with its apex under the line of the cut, and the glass is frequently wedged up on both sides of the ridge, explaining the cause of the double line of fracture which sometimes makes its appearance in polishing out a scratch. This effect may also be exemplified by observing the marks left on a polished glass surface from the light blows of a steel centre-punch. The point of the punch drives in an atom of the glass, and the fracture extends some distance into the interior, expanding downwards in the form of a truncated cone. The polariscope shows that the conical centre is in a state of compression, and that the surrounding exterior portion of the glass is also under strain.

The smooth, round edge of a glazier's diamond, when drawn over a polished glass surface, burnishes down and compresses the glass beneath the cut, and in the case of thin sheets the wedge-like force of the compressed line splits the glass nearly through; but when the glass is thick and rigid, as plate-glass, unless the sheet is bent back and broken through immediately after the cut, greater difficulty will be experienced if allowed to remain for a time, for the compressed line of glass will speedily tear up the portion on both sides, leaving a wide ragged groove in place of the original clean and scarcely visible line.

THE EXCISE LABORATORY.

REPORT FROM THE PRINCIPAL TO THE COMMISSIONERS OF THE INLAND REVENUE, 1865.

In my last Report I alluded to the fact that, owing to recent legislation, the business of the laboratory had altered considerably in character, and that, although the aggregate number of samples examined during the year was much less than the number examined in the previous year, the amount of work performed was much greater. In reverting to this subject, at the risk of being charged with giving undue prominence to it, I am actuated solely by a desire to show that the operations of my department, as subsidiary to a highly organised system of levying and securing a large revenue, have not lessened, but are steadily increasing in importance. That this should be the case is not surprising, as the invention and adroitness brought to bear on the acquisition of wealth are daily becoming more refined, and more adopted by enterprising per sons. Occasionally bold attempts are made to circumvent the revenue under the guise of new and legitimate objects of trade, whilst it not infrequently happens

that complaints are made that the existing fiscal restrictions imposed on the production and assessment of dutiable commodities are unnecessarily stringent, and that a relaxation of such restrictions might safely be allowed. Some of these complaints are, no doubt, well founded and deserving of serious attention, but others are insidious, and the pleas upon which they are based require to be examined with the utmost care, under the guidance of the laws and regulations relating to the collection of the revenue, and also by scientific investigations of the modified processes which may be proposed as beneficial to trade, but which, if sanctioned, might lead to frauds on the revenue. Thus, the number of samples analysed does not give a full idea of the extent of the business of the laboratory, as the researches and investigations undertaken for special objects, and which demand much time and thought, are not included. As an instance, it may be proper to mention the following case, which is now depending :-The hop planters of Kent, being desirous to avail themselves of duty-free tobacco for the purpose of destroying the insects which infest the hop plant, memorialised Government on the subject, and the question being submitted to me, a series of experiments were at once commenced to discover some mode by which the extract of tobacco intended to be used might be rendered unfit for the purposes of fraudulent tobacco manufacturers, without causing it to be injurious to the hop plant. The problem may appear simple, but it was soon found to be very difficult of solution, and all the substances hitherto tried, which, when added to the tobacco extract, could not again be separated effectually, and which would prevent an improper use of such extract, have proved to be injurious to vegetation. Experiments are still going on, and I hope to be able soon to surmount the difficulty.

During the last financial year the Act allowing dutyfree malt to be used in the feeding of animals came into operation, and up to March 31 last 519 samples of mixtures of malt and linseed prepared for the purpose mentioned, and 365 samples of ground linseed alone, had been examined in the laboratory; and it is satisfactory to be able to state that, with two or three exceptions, the whole of the samples were found to be totally unfit for the brewing of beer, thus proving that the revenue derived from malt is not, as it was by some feared it would be, endangered under the provisions of the Act in question.

The stringent measures adopted by the Customs to prevent the importation of simulated wines are still continued, and 182 samples have within the year been examined, of which 102 were found to be composed chiefly of factitious wine, whilst nearly the whole of the remaining 70 were of very low value, and, although genuine wine predominated more or less in their composition, they still contained considerable proportions of spurious wine. There can be no doubt but that these made-up liquids would, but for the energetical action of the Customs, have passed into consumption either per se as sherry, or mixed with genuine wine.

Within the past year two manufactories have been established in London for the purpose of preparing glucose or starch sugar for the use of brewers, and as this sugar differs considerably both in value and character from cane sugar, to which alone the existing rates of duty apply, it has become necessary, for the purposes of assessment, to determine the ratio of dutiable value of the two descriptions of sugar, and for this end 12 samples of glucore have been analysed.

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29,195,000

Pounds Weight of Tobacco cleared for consumption

in the

United Kingdom.

23,096,281

Weight of Tobacco yearly consumed per bead of the population. lbs. OZS. O 134

27,734,786

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35,413,846 37,636,240

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1861

8364

3045

22

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11360

1863 6309 1864 8388

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8588 10708 2120

Decrease.

71 2772

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In the educational branch of the laboratory ten young officers have, since the date of my last Report, completed a course of study in chemistry, and in their final examination by Dr. Hofmann they acquitted themselves in such a manner as to draw from that gentleman a very high encomium. This satisfactory result is mainly due to the intelligence and assiduity of the students themselves, who, in common with their predecessors, have shown a desire to profit to the utmost by the opportunity afforded them of obtaining scientific knowledge, and have evinced an earnest and praiseworthy determination to merit the approbation of the Board. Fiftynine students have now passed through a course of education in chemistry, and it is perhaps not too much to say that they form a valuable reserve from which officers may be selected to assist in securing the revenue in those cases in which it may be advantageous to make their scientific knowledge available. At the present time only six students are under instruction, as owing to the limited space at the disposal of the department, and the increase of the practical business of the laboratory, it was found difficult to spare room for

more.

During the period to which this Report relates four teen examiners have received in the laboratory a month's instruction in the modes of detecting the adulteration of articles subject to revenue duties; 170 of these officers, whose position in the service is highly onerous and demands much intelligence and practical knowledge, have passed, on the whole, with great credit through my department.

Tobacco. The condition of the trade in this important commodity, so far at least as relates to the question of adulteration, continues in a most healthy state; it cannot, of course, be supposed that an article upon which is imposed a duty of about 500 per cent. on its value, should escape the attention of the smuggler or the adulterator, and it can only have been by well-directed and sustained efforts that frauds on the tobacco revenue have been kept down to a minimum which is insignificant when compared with the large yearly duty derived

1863 Population estimated according to the percentage increase during the decennial period from 1851 to 1861. A few cases of the adulteration of tobacco with liquorice have been detected during the past year, but the quantity of liquorice used was very small. In two instances which occurred in London the tobacco contained not more than 1 per cent. of the illicit ingredient. The practice of illegally using liquorice and other saccharine matter still lingers in Ireland, but the numerous detections which were some time ago made, and the penalties imposed, appear to have had a salutary effect, timidly, and not in that gross and daring manner as the fraud, when now committed, seems to be done which was the case when the offenders were under the impression that the Revenue possessed no satisof the fraud. factory means of proving, by analysis, the commission

As in previous years, I have myself closely inspected kingdom, and I am in a position to say, from my own a large number of the tobacco manufactories in the observation, that the adulteration of tobacco is now

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Manufacture of Arsenic Acid.-Girardin suspends powdered arsenious acid in water, and passes chlorine into the mixture, by which he soon obtains a clear solution of arsenic acid in hydrochloric acid. By evaporating this solution a mass of arsenic acid containing no trace of arsenious is procured. As it is difficult to keep any considerable amount of arsenious acid in suspension solution of that acid in hydrochloric, and pass the in water, the author finds it better to make a saturated chlorine into such solution while hot. The stream of chlorine is stopped when a little of the fluid neutralised with potash no longer gives a green precipitate with bichromate of potash, thus showing that all the arsenious acid has been converted. The hydrochloric acid may then be recovered by distillation, and the syrupy solution of arsenic acid left in the retort evaporated.

NEWS

PROCEEDINGS OF SOCIETIES.

ROYAL INSTITUTION OF GREAT BRITAIN. Weekly Evening Meeting, Friday, April 7. H.R.H. THE PRINCE OF WALES, Vice-Patron, in the Chair. On the Combining Power of Atoms. By Dr. A. W. HOFMANN, F.R. S. (Continued from page 169.)

In the preceding remarks, I have submitted to you an extensive series of examples taken from different pages in the vast volume of chemistry, which appear to indicate that oxygen combines atom by atom, that nitrogen enters the compound freighted with one atom of hydrogen, and, lastly, that carbon cannot join the concern except with a capital, so to speak, of two atoms of hydrogen. Supposing, for a moment, that this rule could be established without a single exception throughout the whole range of chemistry; are we enabled to assign a probable reason for this peculiar behaviour of the oxygen, nitrogen, and carbon atoms?

To answer this question we must commence by considering for a few moments some of the simplest compounds of the elements concerned.

Here we have four glass tubes surmounted by large globes. The first of these contains hydrochloric acid, the compound of hydrogen with chlorine; the second did contain the vapour of water, -the compound of hydrogen with oxygen-but which is now condensed to small drops of fluid water deposited on the sides of the globe; in the third vessel we have the compound of hydrogen with nitrogen, ammonia; while the last is filled with one of the compounds of carbon with hydrogen, viz., marsh-gas. These four compounds, all transparent and colourless,

we distinguish by the simplest experiments. On opening the sealed tubes of the vessels under mercury, no change takes place in the case of hydrochloric acid, ammonia, and marsh-gas, while the mercury immediately rises and fills the globe containing the condensed water vapour. When the remaining three vessels are now raised, so as to allow the broken points of the tubes to dip in a layer of water floating on the mercury, the liquid rushes into the globes containing hydrochloric acid and ammonia; of the two solutions thus produced by the absorption of the gases, the one containing the hydrochloric acid reddens blue litmus; the other, formed by the absorption of the ammonia, changes red litmus to blue. The marsh-gas differs from all the others by its insolubility and by its inflammability. Indeed, if the globe be broken and a light applied, the gas burns with a feebly luminous flame.

Nor are the differences observed in the structure of these four hydrogen compounds less characteristic, although they cannot be so easily demonstrated by experiment,-at all events, within the limited time at my disposal. Indeed, to give you an idea of their structure which is necessary for our purposes, I must be permitted to borrow a leaf from the book of the Wizard of the North, and to avail myself of a simple mechanical contrivance devised for that purpose. Let these four tin boxes represent two volumes of hydrochloric acid, water-gas, ammonia, and marsh-gas. We wish to know the quantities of hydrogen contained in two volumes of each of these four bodies, and we find that out of the two volumes of hydrochloric acid we are enabled to pull one volume of hydrogen; out of the same volume of water-vapour, two volumes of hydrogen; out of the same volume of ammonia, by a mechanical contrivance of the simplest description, three volumes of hydrogen; and, lastly, out of two volumes of marsh-gas, four volumes of hydrogen.

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ammonia, one of nitrogen; and, lastly, from the two volumes of marsh-gas, an amount of carbon which provisionally I may be permitted to represent by one volume, since, owing to the non-volatility of the carbon, the volume of the carbon-vapour has not yet been ascertained.

FIG. 2.

FIG. 3.

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In the second column of the diagram are given the compounds of these four elements with chlorine, and exactly as we have seen them combining respectively with 1, 2, 3, and 4 volumes of hydrogen, we now find them associated with 1, 2, 3, and 4 volumes of chlorine. Again, in the third column we have the series of sodium compounds of these elements, and although in this case we must be careful not to speak of volumes of sodium-vapour, since chemists have not as yet obtained sodium-gas in the pure state, we perceive at all events from the diagram that one volume of oxygen fixes exactly twice, one volume of nitrogen exactly three times the quantity of sodium which is combined with one volume of chlorine.

The study of elementary gases has led chemists to the unanimous opinion that equal volumes of these different gases contain an equal number of the smallest particles or atoms. Numerous theoretical considerations and numerous experimental inquiries inevitably lead to this result, which is now a generally received truth. If equal volumes of

different gases be submitted to the same pressure they contract to an equal extent, and if they are equally heated they expand equally.

We have an apparatus (Fig. 5) so disposed as to permit us to establish this point experimentally. It consists of a kind of double U tube, with one long and simple limb, and one short limb bifurcated into two branches, each of which is provided with a stopcock. These short limbs are, moreover, surrounded by a glass cylinder. Near the bottom of the apparatus another stopcock is placed, enabling us to empty the apparatus. The three limbs of the instrument being filled with mercury, we introduce into the stopcocked limbs the gases to be examined, into the one hydrogen, and into the other oxygen, care being taken to have as nearly as possible equal volumes of the two. These volumes being marked by caoutchouc rings, we pour mercury into the long open limb, and we find that the mercury column thus obtained compresses the two gases to an exactly equal extent. Again, on letting out mercury through the bottom sropcock, so as to lower the column and diminish the pressure, we observe that both hydrogen and oxygen undergo equal dilatation. And so, again, we are enabled to prove the expansion and contraction of the two gases to be equal, if the glass cylinder surrounding the bifurcated limb of the apparatus be filled alternately by hot steam or cold air.

Now, if equal volumes of the elementary gases contain an equal number of atoms, it is obvious that

The chlorine atom combines with 1 atom of hydrogen,

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19 oxygen nitrogen and since there are reasons for believing that the quantity of carbon existing in two volumes of marsh-gas (but which, as I have pointed out, has never been obtained in the gaseous state) represents the carbon atom, we may add that

The carbon atom combines with 4 atoms of hydrogen. And in a similar manner we may say that the atoms of the four elements in question, when uniting with chlorine, are found to be capable of fixing 1, 2, 3, or 4 atoms of chlorine.

These observations, which, if time permitted, might be considerably expanded, lead us to a very important distinction of elementary atoms, which is based upon their atom-fixing capabilities, more shortly expressed, upon their combining powers.

If the atom-fixing power of the chlorine atom be taken as standard of comparison, we are compelled to assign to the oxygen atom the twofold, to the nitrogen atom the threefold, and to the carbon atom the fourfold atom-fixing power; or, looking at this question from a different point of view, we find that one atom of oxygen is performing the work of two atoms of chlorine; one atom of nitrogen, that of three; one atom of carbon, lastly, that of four atoms of chlorine. Hence we distinguish the chlorine atom as univalent, the atom of oxygen as bivalent, that of nitrogen as trivalent, and, lastly, the carbon atom as quadrivalent.

With the recognition of these different combining powers in elementary atoms we have made a very considerable step towards the solution of the question which presented itself in the earlier part of this discourse-viz., How is it that the oxygen atom is fixed directly, the nitrogen atom together with one, the carbon atom, lastly, together, with two atoms of hydrogen? This peculiar mode of combination is the necessary consequence of the special atom-fixing capabilities of the oxygen, nitrogen, and carbon atoms; and this I believe I can show you by a very simple contrivance. I am again tempted to rely entirely on mechanical means of elucidating the subject, and I will on this occasion, with your permission, select my illustration from that most delightful of games, croquet.

Let the croquet balls represent our atoms, and let us distinguish the atoms of different elements by different

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