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Again, the authors estimated that in the experiments of the Rev. Mr. Smith of Lois Weedon, on the growth of wheat year after year on the same land, without manure, there had been an annual extraction from each acre of land of about three and a half times as much phosphoric acid, about seven times as much potass, and about thirty-seven times as much silica, as there would be in the ordinary course of practice; yet, after some fifteen years the crops at Lois Weedon were said not to be at all failing.

The authors did not recommend such exhaustive practice as that quoted from their own, or the Rev. Mr. Smith's experiments. But the instances given showed the capabilities of certain soils; and in one case the conditions under which the point of comparative exhaustion had been reached. It was, of course, impossible to state the limits of the capability of soils generally, so infinitely varied was their composition; but it would be useful to give an illustration on this point. Reckoning the soil to be one foot deep, it was estimated that it would require, of ordinary rotation with home manuring and selling only corn and meat, about 1000 years to exhaust as much phosphoric acid, about 2000 years to exhaust as much potass, and about 6000 years to exhaust as much silica, as, according to the average results of forty-two analyses* relating to fourteen soils of very various descriptions, had been found to be soluble in dilute hydrochloric acid. Many soils had, doubtless, a composition inferior to that here supposed. In a large proportion, however, the amounts of the above constituents assumed to be soluble in dilute hydrochloric acid would probably be available for plants long before the expiration of the periods mentioned; whilst, in a large proportion, there would still be further stores eventually available within a greater or a less depth from the surface.

But the exhaustion of mineral constituents by the sale of corn and meat alone was in reality not so great, in the ordinary practice of this country, as has been assumed for the purpose of the above illustrations. Where there was no purchase of cattle-food, or of artificial or town manures, the sales of corn and meat would on the average be much less than were taken in the authors' estimates; and where such materials were purchased with any degree of judgment in the selection, there would always be much more phosphoric acid (otherwise the most easily exhausted constituent) so brought upon the land, than would be obtained from it in the increase of produce yielded; in fact, under such conditions, in many soils potass was more likely to become deficient. Again, by no means the whole of the mineral constituents sent from the farm in the form of corn and meat will reach the sewers of our towns, and thence our rivers; a not inconsiderable portion finding its way back to the land in some form; in addition to which, imported corn, meat, and other materials will contribute something to the restoration of our own cultivated land. It is at the same time certain that so much of the refuse matters of our towns as becomes diluted with water in the degree recognized under the present sewerage system will be applicable as manure, on the large scale, only to succulent crops, and especially to grass-land; and, so far as this is the case, they will of course not directly contribute to the restoration to the land under tillage, of the mineral constituents sent from it in its produce of corn and meat. When other descriptions of produce than corn and meat, such as roots, hay, or straw, are largely sold, compensation is generally made by the return to the land of stable- or town-manures of some kind. If this be not done, the loss of mineral constituents may indeed be very considerable.

In conclusion, whilst the authors insisted upon the importance of applying to agricultural purposes as much as possible of the valuable manuring matters of our towns, they at the same time believed that modern practices, taken as a whole, did not tend to exhaustion in anything like the degree that had been supposed by some.

On Purifying Towns from Sewage by means of Dry Cloaca.
By Dr. J. H. LLOYD.

On the Proportion of Tin present in Tea-Lead. By Dr. S. MACADAM.

*The accuracy of some of these analyses, however, is admitted as open to question: sce Report by Magnus, Ann. d. Landwirthschaft, xiv. 2.

On the Proportion of Arsenic present in Paper-Hangings.

By Dr. S. MACADAM.

The author had been led to the investigation of this subject by hearing of cases of arsenical poisonings through remaining in rooms with green paperhanging In all these cases of which he had heard, the patients soon recovered on beig removed from one room to another. The question whether the arsenic in grea paperhangings was injurious to health very much resembled the question regarding fead, in which it had been stated that a small quantity, though not affecting one person, might act very injuriously upon another. In most of the green paperhangings the arsenic was present in the condition of a rough powder. In some cases the paper was glazed, which had the effect of protecting the arsenic. He had examined several green flock papers, and as a general rule he believed they did not contain arsenic; but all the common descriptions of green paperhangings did. He purchased two packets of envelopes, the bands around which were coloured green. In these two bands he found 33 grains of arsenic. The common green paperhangings contained an amount of arsenic varying from 1 to 40 grains per square foot. Taking the mean quantity at 20 grains, a large-sized room would per haps contain 20,000 grains of arsenic in the paper; a small room 10,000 grainsquantity capable of producing very serious symptoms. With regard to the mode in which this arsenic could be introduced into the system, it was a question whe ther arsenic volatilized at ordinary temperatures; but he thought it was not carrying the point too far to suppose that during the damp condition of the paper when being hung, a certain proportion of the arsenic was carried off with the water in the shape of vapour. It was likely to occur also during the night, when the exbalation of the animal system would produce a moisture on the walls as well as the windows, and when a draught was created by the opening of the door in the morning a certain portion of the arsenic might be volatilized. It was possibly more liable to be disturbed by mechanical action, such as dusting, or the rubbing of dresses against the wall, or the grazing of bedhangings against the paper. In such cases the arsenic fell in fine dust upon the carpets, and whenever the carpets were brushed the small particles would fly about and be inhaled. He had not met with any case of death through arsenical poisonings from paperhangings, but he believed it was a medical fact that arsenic taken into the system, even in very small quantities, would soon undermine the health.

On an Economical Mode of boiling Rags, &c. with Alkaline Ley.
By Dr. S. MACADAM.

On the Separation of Ammonia from Coal-gas. By W. MARRIOTT.

In the manufacture of coal-gas a large quantity of ammonia is generated along with the permanent gases. The greater portion of the ammonia is separated by cooling or scrubbing, but still a considerable portion passes through the lime or oxide purifier, and so passes along with the gas as caustic ammonia.

Gas-managers are fully aware of the desirability of removing the ammonia, and many processes have been devised for this purpose, some of which are in operation in different gas-works.

Of all the substances which have been used for this purpose sulphuric acid is perhaps the simplest in its application, and, space and economy considered, the quickest in its removal of the ammonia. But there is one great objection in the use of strong sulphuric acid, namely, that it diminishes the illuminating power of the gas by absorbing the rich hydrocarbons.

If

gas is allowed for a length of time to pass through sulphuric acid, a point is reached when no more of the hydrocarbons are absorbed, after which the gas may be passed through the acid without injury to its illuminating power.

Acid so prepared is saturated with carbonaceous matter, and if filtered and evaporated to dryness, a mass of carbon is left in the dish.

Now, sulphuric acid so prepared, though it has lost its injurious action on the gas, retains its affinity for the ammonia.

It is the above principle of saturating the sulphuric acid with carbonaceous

matter which is applied in the material we now use extensively for separating the ammonia from coal-gas, with this improvement, that the acid instead of being in the liquid state is solid, and is at once in the purifier converted into crystallized sulphate of ammonia.

In saturating sulphuric acid with carbon it is not necessary to use the gaseous hydrocarbons, as almost any vegetable matter will do; sawdust is used. The material is prepared by heating together, at a temperature of about 280° Fahr., equal weights of sulphuric acid, sp. gr. 1700, and sawdust.

At that temperature the organic matter of the sawdust is broken up, and the carbon eliminated solidifies the acid; at the same time the acid dissolves as much carbonaceous matter as it will take up.

The author cannot say what is the organic compound dissolved by the acid, only that in this form of saturation the acid does not in the least injure the illuminating power of the gases passed through it.

On account of the immense surface of acid exposed to the gas when so prepared, we are not surprised to find that the ammonia is separated from the gas instantly it comes in contact with it; in fact, where we are passing from 1 to 3 millions feet of gas in 24 hours, we cannot detect any ammonia until the material is saturated to within 1 or 2 inches of the surface.

The material being very porous, offers very little obstruction to the passage of the gas, and so scarcely increases the pressure.

All those who are engaged in the manufacture of sulphate of ammonia from the ammoniacal liquor obtained from gas-works, well know the great loss of this salt carried away by the steam, either in evaporating a solution to the crystallizing point, or in passing the ammoniacal vapours through the acid. On the large scale the loss is from 10 to 20 per cent.

In the acid prepared as already stated, and converted into sulphate of ammonia, at the temperature of the gas as it passes through the purifier there is no loss; for every equivalent of sulphuric acid used, an equivalent of sulphate of ammonia is received. In an economical point of view this is a great saving; but there is still further economy in the labour, because the very process of removing the ammonia from the gas converts it into sulphate of ammonia ready for the market.

The material as discharged from the purifier contains from 50 to 60 per cent. of sulphate of ammonia applicable for manure purposes.

The author claimed no novelty, either in the use of sulphuric acid alone or mixed with sawdust, but thought its application as a free acid, when saturated with carbonaceous matter, might be of interest to the Section.

On Madder Photographs. By JOHN MERCER, F.R.S.

On Photographic Spectra of the Electric Light.
By Professor W. A. MILLER, M.D., F.R.S.

The apparatus by which the spectra may be photographed consists of an ordinary camera obscura attached to the end of a long wooden tube, which opens into a cylindrical box, within which is a prism glass, or a hollow prism filled with bisulphide of carbon. If the prism be so adjusted as to throw the solar rays, reflected from a heliostat, upon the screen of a camera, and the wires which transmit the sparks from Ruhmkorff's coil are placed in front of the uncovered portion of the slit, the two spectra are simultaneously impressed. The solar beam is easily intercepted at the proper time by means of a small screen, and the electric spectrum is allowed to continue its action for two or three, or six minutes, as may be necessary. The author did not find that anything was gained in distinctness by interposing a lens of short focus between the slit and the wire which supplied the sparks, with the view of rendering the rays of the electric light parallel like those of the sun, owing to the absorbent action of the glass weakening the photographic effect; the flickering motion of the sparks being magnified by the lens, rendered the lines less distinct than when the lens was not used. Although with each of the metals (including platinum, gold, silver, copper, zinc, aluminum, magnesium, iron), when the spark was taken in air, he obtained decided photographs, it appeared that in each case the impressed spectrum was very nearly the same, proving that few of

and

the lines produced were those which were characteristic of the metal. The peculiar lines of the metal seemed chiefly to be confined to the visible portion of the spectrum, and these had little or no photographic power. This was singularly exemplified by repeating the experiment upon the same metal in air, in a contianous current of pure hydrogen. Iron, for example, gave, in hydrogen, a spectrum in which a bright orange and a strong green band were visible, besides a few faint lines in the blue part of the spectrum. Although the light produced by the action of the coil was allowed to fall for ten minutes upon a sensitive collodion surface, scarcely a trace of any action was procured; whilst, in five minutes, in the air, s powerful impression of numerous bands was obtained. It was remarked by Mr. Talbot that, in the spectra of coloured flames, the nature of the acid did not influence the position of the bright lines of the spectrum, which he found was dependent upon the metal employed; and this remark has been confirmed by all subsequent observers. But the case is very different in the absorption-bands produced by the vapours of coloured bodies,-there the nature of both constituents of the compound is essentially connected with the production of absorptive bands. Chlorine, combined with hydrogen, gave no bands by absorption in any moderate thickness. Chlorous acid and peroxide of chlorine both produced the same set of bands, while hypochlorous acid, although a strongly coloured vapour and containing the same elements, oxygen and chlorine, produced no absorption-bands. Again, the brownish-red vapour of perchloride of iron produced no absorption-bands; but when converted into vapour in a flame, the iron showed bands independent of the form in which it occurred combined. These anomalies appear to admit of an easy expla nation on the supposition that, in any case, the compound employed is decomposed in the flame, either simply by the high temperature, just as water is, as shown by Grove, or in other cases by the reducing action of the burning bodies, which supply the flame, upon the metallic salt introduced into the flame. In the voltaic pile the decomposition must of necessity take place by electric action. The compound gases, protoxide and binoxide of nitrogen, give, when electrified, the same series of bright bands (as Plücker has shown) which their constituents when combined furnish. Aqueous vapour always gives the bright lines due to hydrogen; and hydrochloric acid the mixed system of lines which would be produced by hydrogen and chlorine. The reducing influence of the hydrogen and other combustible constituents of the burning body would decompose the salt, liberating the metal, which would immediately become oxidized or carried off in the ascending current. There was obviously a marked difference between the effect of intense ignition upon most of the metallic and the non-metallic bodies. The observations of Plücker upon the spectra of iodine, bromine, and chlorine show that they give, when ignited, a very different series of bands from those which they furnished by absorption, as Dr. Gladstone has already pointed out; but it is interesting to remark that in the case of hydrogen, which, chemically, is so similar to a metal, we have a comparatively simple spectrum, in which the three principal bright lines correspond to Fraunhofer's dark lines C, F, and G. It was, however, to be specially noted that the hydrogen occasioned no perceptible absorption-bands at ordinary temperatures in such thickness as we could command in our experiments, and the vapour of boiling mercury was also destitute of any absorptive action, although, when ignited by the electric spark, it gave a characteristic and brilliant series of dark bands. The following experiment suggested itself as a direct test of Kirchhoff's theory. Two gas-burners, into which were introduced chloride of sodium on the wick of the spirit-lamp, were placed so as to illuminate equally the opposite sides of a sheet of paper partially greased. The rays of the electric light screened from the photometric surface, suitably protected, were made to traverse one of the flames. If the yellow rays of the light were absorbed by the sodium flame, the light emitted laterally by the flame should be sensibly increased. The experiment, however, failed to indicate any such increase in the brilliancy of the flame, possibly because the eye was not sufficiently sensitive to detect the slight difference which was to be expected.

On Atmospheric Ozone. By Dr. Moffat.

The results given were from the observations of ten years, taken at Hawarden at a height of 260 feet above the level of the sea. The quantity of ozone is greater with

decreasing readings of the barometer and when the readings are below the mean, than with increasing readings and when they are above the mean, and greater when the range of the barometer and the number of its oscillations are above the mean. It is greater when the mean daily temperature and dew-point temperature are above the mean. Ozone is at a minimum with the wind from points north of S.E. and N.W., and at a maximum with the wind from points south of these; it is also at a maximum when the wind is above its mean force. When rain is above the mean quantity ozone is also above the mean, and also with hail; but it is below the mean with snow and sleet. With fog it is below the mean, above it with cirri, halos, aurora, and the zodiacal light, but below it with thunder. It is in greater quantity with negative than with positive electricity. Ozone periods so frequently commence with the wind from S.E. points of the compass, and so often terminate with the wind in N.W. points, that these may be called their points of commencement and termination. They may also be said to commence with decreasing readings of the barometer and increase of temperature, and to terminate with increasing readings and decrease of temperature. The quantity of ozone is also greater in the night than in the day. It is greater with new and full moon than during the first and last quarters; and it also varies with the seasons, being greater in the winter and spring months than in summer and autumn. The quantity of ozone varies with the locality; it is greater on the sea-shore than at inland places, and it also increases in quantity with increase of elevation. It is greater in the open country than in towns and villages; and it is at 0 in drains and cesspools and their vicinity, and, in short, at every place where the products of putrefaction or combustion are in sufficient quantity to decompose it. Although these results are from Hawarden observations only, they are supported by observations taken at other places. Differences at individual stations may be attributed to purely local causes. Ozone is a highly oxidized body, and it is easily decomposed by oxidable substances. If test-paper prepared with iodide of potassium be exposed in a locality where these substances are at a minimum, it will in time become brown, and ozone will be at its maximum. If a similar paper be placed in a locality where the quantity of oxidable substances is at its maximum, it will remain white, and ozone will be at a minimum; and if a brown paper be put in the latter place, it will lose its colour, sulphuretted hydrogen being the decolorizing agent. On the sea and the sea-shore ozone is at its maximum, because the products of putrefaction are there small in quantity, and the wind which blows over the ocean is the ozoniferous current. On the land the products of decomposition are at their maximum, hence the current of air that passes over it is non-ozoniferous. Indeed all the conditions of an ozone period are those of the equatorial or ocean current of the atmosphere, and the conditions of a no-ozone period are those of the polar or land current.

Medico-meteorological results give the maximum of diseases with the ozoniferous current, and the maximum of deaths with the no-ozone current, but the diseases may be attributed rather to the vicissitudes of weather than to ozone. As the land or polar current of the air is the lower strata in motion, and the ocean or equatorial current the motion of the higher strata, there ought to be an analogy in a medicometeorological sense between them, and so we find that the maximum of deaths takes place in the lower strata with minimum of ozone, and the minimum of deaths in the higher strata with maximum of ozone. The calm is also a no-ozone period. During continued calms the products of putrefaction accumulate in the lower strata of the atmosphere and produce diseases of an epidemic nature. A cholera period is a calm and a no-ozone period; and cholera periods terminate with the setting in of the ozoniferous current. In conducting ozone observations, it must be borne in mind that light causes coloration of the test-papers, and that moisture, sulphuretted hydrogen and ammonia cause loss of colour.

On Sulphuretted Hydrogen as a Product of Putrefaction.
By Dr. MOFFAT.

The author had enclosed portions of animal and vegetable matter in tin boxes, and through slits in the lids, test-papers prepared with carbonate of lead and with iodine were introduced to half their length. The action of sulphuretted hydrogen was decisively shown, both in the case of the animal and the vegetable matters.

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