inch. They were laminated, of a grey color, and had much the appearance of volcanic tufa; they consisted principally of carbonate and sulphate of lime with a little magnesia, protoxide of iron, silica, and carbonaceous matter-the last two, the silica and carbonaceous matter, probably chiefly derived from the smoke of the engine and the dust in the air. From the engineer's report it would appear that the thinnest-the incrustation of about one-tenth of an inch-had formed in about a week, during which time the locomotive had run about 436 miles, and consumed about 10,900 gallons of

water.

ON THE SUGAR PRODUCE OF THE
SOUTH OF SPAIN, CHIEFLY IN
CONNEXION WITH THE EMPLOY-
MENT OF THE ACETATE OF LEAD
AND SULPHUROUS ACID AS PU-
RIFYING AGENTS.

BY DR. SCOFFERN.

ON the southern coast of Spain, in a region limited by Almeria on the east and Malaga on the west, bounded on the north by mountain ranges and on the south by the Mediterranean, is a tract of land which, so far as its climate and productions are concerned, may be aptly denominated tropical. In it, the date, palm, indigo, cotton, and sugar-cane flourish with vigor, yielding products equal in both quantity and quality to those of the tropics themselves.

The sugar-cane, first introduced by the Arab conquerors, is not only consumed in large quantities as a dessert, but also gives rise to a considerable manufacture of raw and refined sugar, a circumstance which beyond Spain itself seems to be very little known.

There is, perhaps, no example on record of any operation involving a commercial result attended with such an enormous destruction of material as the operation of extracting sugar from the cane. One portion of this loss is due to mechanical, another to chemical causes. The sugar-cane has been stated by most writers who have found opportunities of practically examining the subject to contain no more than 10 per cent. of solid non-saccharine matter, leaving 90 per cent. of juice to be extracted. Of this 90 per cent. most writers concur in testifying that in practice scarcely 50 per cent. are actually obtained; at least this is the case in the British West Indian possessions. Cane juice itself has usually been stated to contain from 17 to 23 per cent. of crystalline sugar, of which scarcely 7 per cent. in practice is actually extracted.

Considerable doubts having been expressed as to the statements of the amount of juice in the cane, and sugar in the juice, I have lately gone through a series of experiments having for their object the settlement of the doubt, and with the result of amply confirming the testimony of other experimenters. Having operated on canes from various parts of this district, by slicing themexhausting first by hot water and then by hot alcohol, and finally drying, I obtained as a mean result about 10 per cent. of woody or insoluble matter-whilst the sugar extracted and crystallised ranged from 17 to 23 per cent., as had previously been stated. It would consequently appear that 40 per cent. of juice is actually lost in the practice of our West India workings; and now arises, as a most important consideration, the question as to what extent this loss is inevitable, and to what extent it might have been obviated by altered machinery or improved manipulation. Instead of 50 per cent. of juice extracted, 70 per cent. is much nearer the average amount yielded by the sugar-mills of this coast, although occasionally the result is as high as 75 per cent., and this, in some cases, with mills of very inferior construction. The cane, however, is passed between the rollers of the mill four times, until the refuse or megass, as the pressed cane is called, has been reduced to a state of disaggregation resembling ground tan, whereas the West Indian cane refuse is represented to be in the form of long strings, a sufficient proof that the pressure applied has been very inadequate. After the cane has finally left the mill it is immediately, in the Spanish sugar regions, subjected to the operation of pressing, sometimes by the agency of a screw, but in many cases by hydrostatic force. By the latter method, I have seen 13 per cent. of juice extracted from megass which had already yielded up 73 per cent. of juice to the mill, thus elevating the total quantity extracted to 86 per cent. out of the original 90, and consequently as a manufacturing operation leaving very little more to be desired. The hydrostatic press I consider to be an apparatus which is indispensable to the economy of every sugar estate: not only does it largely contribute to the amount of juice extracted, but what is most remarkable is, the juice resulting from hydrostatic pressure of megass is invariably, so far as my observations have gone, richer in sugar than juice yielded by the mill-a fact which seems to be explicable only on the supposition that the hydrostatic press, by virtue of its great power, is enabled to extrude those particles of sugar which microscopic exa

mination demonstrates to exist in the cane | highly antagonistic to fermentation. Anin the solid and crystalline form.

other speculative fear was that danger might arise from the lead employed: this fear, too, practice demonstrates to be entirely without foundation, for not only is the sulphite of lead most easily removed,— but even were it to remain no injury could supervene, inasmuch as this agent is as harmless as chalk.

Dr. GREGORY stated that he had made experiments on the sulphite of lead formed in this process. He admitted that an infinitely small proportion might still remain in the sugar, but that he considered it quite innocuous. He had indeed fed rabbits and dogs with food which had been united with this sulphite of lead, and the result was that they thrived amazingly, showing no symptom of any of the known effects of lead. Dr. Gregory also remarked that in testing sugar for lead with the hydro-sulphuret of ammonia, iron was often mistaken for the former metal.

Dr. CHRISTISON contended that we had no evidence that the sulphite of lead was innocuous. It was true that in cases of poisoning by carbonate of lead sulphuric acid was administered to convert it into the comparatively insoluble sulphate; but this was a case widely different from the slow

The subsequent stages of the sugar manufacture as carried on in Spain do not materially differ from those in operation in Cuba, and many other tropical countries. The juice is defecated or purified by lime, skimmed, evaporated to the requisite degree, and poured into earthenware moulds, the contents of which are finally exposed to the operation of claying. In one manufactory, however, at Almunecar, lime is no longer used on account of its well-known injurious effects on sugar:-no other agent having been substituted in its stead, but sole reliance being placed on the coagulation by heat of albuminous matters present in the juice, and their final removal by skimming. Under this system of manufacture the sugar produced is light colored, but badly grained, and the unseparated albuminous matters are present in such quantity that every 100 parts of the concentrated saccharine juice as it comes from the teache, or last evaporating pan, yield only 40 parts of crystallised sugar on cooling, the other 60 per cent. remaining in the condition of molasses perfectly uncrystallisable until some adequate means for defecation can be resorted to. The chief object of my residence in this sugar district was to superintend the erection of ma-accumulation of lead in the system. He chinery for manufacturing sugar by my own process. The site of our operations is Montril, about forty-five miles south of Granada,—in a manufactory furnished with apparatus of the rudest character. Up to this period (July 9) our own vacuum apparatus has not been sufficiently advanced to enable us to pursue our operations by its aid; nevertheless, owing to the superior defecating power of the subacetate of lead, we have, even with the old and rude machinery, obtained a result of more than 16 instead of 7 per cent. of sugar. Our striking teaches, or final evaporating pans, we were under the necessity of removing in order to afford the requisite space for our own machinery; hence we were reduced to the necessity of concluding our process of concentration in a brass pan of conical form and holding about 600 imperial gallons, thus materially increasing the difficulty of the evaporative process. Hitherto only one-sixth per cent. on the juice of subacetate has been used, but I imagine the quantity may be advantageously increased. As filtration is indispensable for the conducting of this process, considerable fear was entertained lest fermentation might supervene. This fear, however, practice has demonstrated to be groundless, inasmuch as we possess in sulphurous acid an agent

adduced some examples of exceedingly small doses of lead being taken in water for more than twelve months before its evil effects became apparent. He, therefore, thought it yet remained to be proved that the sulphite of lead was without action on the system, since we know nothing of the influence of the solvents it would meet with in the system, or of the influences of vital action. Rabbits, he was prepared to say, should be entirely rejected in these inquiries, since he had found that they were unaffected by many poisons. Dogs and cats were the only animals which could, from their internal structure, be regarded as representatives of the human system in such investigations.

ON AN ACCELERATING PROCESS
IN PHOTOGRAPHY.*

BY J. MIDDLETON, ESQ., F.G.S.

THE following method of preparing sensitive paper may, perhaps, be welcome to photographers on account of the great sensibility which it confers; it has, moreover,

the additional recommendation of being very simple and constant in its results.

I beat up albumen of the egg of the duck until it becomes liquid, and then mix it with

Philosophical Magazine.

affords an advantageous opportunity of calling your attention to questions which must unquestionably depend for solution on the mutual exertions of science and practice. For I hold it to be certain that the two must go together, and that though some of the facts we require may be determined in the laboratory, there are many questions which, though suggested by science, can be established only as facts by

water in the proportion of 80 grains of the former to an ounce of the latter. I add to this solution iodide of potassium in the proportion of 25 grains to the ounce. Prior to the application of this solution, wash the size from the side to be rendered sensible, by means of a camel's-hair brush, and when dry, I float the paper on the solution, for from three to four minutes, and when drained and dried I lay it aside for use. When about to be used for taking a pic-experiments in the field, performed with ture, the paper, prepared as above described, is to be washed with aceto-nitrate of silver, in the proportion of 60 grains of nitrate and 80 grains of acetic acid to an ounce of water (Talbot's strength). I apply the solution with a glass rod, using about 40 grains of it to a quarto page, and allow the paper to dry in the dark. It is now ready for the camera. While applying the sensitive coat, as also while bringing out the picture, I take the precaution of using a yellow light. I find that from ten to fifteen seconds is, with ordinary sunlight, sufficient exposure, the latter being generally too long.

When the picture has been taken, no trace of it appears on the paper, but it soon comes out on the application of a saturated solution of gallic acid. I turn up the edges of my paper and pour on the solution until the paper is entirely covered, and keep it so until the picture has come out sufficiently, when I fix it in the usual way.

If we

every attention to care and accuracy. I hold also that neither of these methods of experiment will in themselves suffice; they must go hand iu hand if our results are to be of value. Separately the chances are that they lead to mere speculations, of which science will supply one set and practice the other; for you must allow me to say that practice has abundance of speculations of its own, which are often much wilder than those on which science ventures. In discussing the general questions of the economy of manures on the present occasion, I must be contented to do so in a general manner, as your time will not permit me to go into any details, and I shall advert, in the first place, shortly to the general properties of manures. examine then any of our common plants, we find it to be composed of a considerable number of chemical substances. These substances may be divided into two great classes, separable from one another by a I find that if bromide of potassium be very simple experiment, which is neither substituted for the iodide, in the first pro- more nor less than burning the plant. cess, a picture is obtained; but the time When this is done we obtain its ash, conthen required for exposure is about one taining the whole of one of these classes; minute. Again, bromide or chloride of the other has, in the process of burning, potassium does not serve to accelerate as in passed into the state of gases, and so esthe ordinary processes, but the contrary; caped the observation of our unassisted gallic acid, too, added to the acetonitrate, senses. The former of these are called the destroys sensitiveness. I find, also, that if mineral or inorganic constituents of the the albumen be dried, and afterwards dis- plant, the latter the organic constituents, solved again and used as above described, because they are peculiarly present in all it has lost its photographic value-a cir- organised beings. The latter of these cumstance which would seem to indicate that classes is a limited one, and contains only photographic properties are connected with four substances-carbon, hydrogen, oxygen, or dependent on molecular arrangement. and nitrogen. The former is much more The employment of albumen in photo-extensive, and comprehends a considerable graphy is not new; it has not, however, so far as I am aware been used in the precise way or with the effect stated above. Agra, 18 June, 1850.

number, of which the most important are sulphuric acid, phosphoric acid, lime, magnesia, potassa, and soda. Now the existence of the plant depends upon its obtaining all these, as well as one or two less important substances, in sufficient quantity; without these it cannot flourish, and just in proportion to the the amount in which they are supplied will be the luxuriance of its growth. I say the growth of the plant will be proportional to the supply of these constituents. This statement, however, is

not to be taken in its widest sense, because valuable matter. To obviate this, however, Nature has fixed a certain limit beyond Nature has so arranged it that these conwhich no supply of these substances, how-stituents exist in the soil in the state of inever liberal, will raise its growth, but up to that limit the statement is substantially correct. From whence, then, is the plant to derive these substances? And in answering this question it is necessary to distinguish between the two classes of substances to which I have already referred, and to inquire separately into the sources of each.

soluble compounds, which under the influence of air and moisture, gradually undergo a series of very complex decompositions, which slowly liberate the constituents, as they are required to support the life of the plant. But Nature has fixed a limit to this change, and has caused these constituents to become soluble with extreme slowness only, and in no greater quantity than is requisite for supporting that amount of vegetation which the general economy of the globe requires.

Now, the whole principle of cultivation is to obtain, by proper treatment, from a given surface of land a greater amount of vegetation than it is capable of producing in a state of nature.

Of the organic constituents there can be but one source, the soil namely, which to be fertile, must contain the whole of these substances in greater or less quantity. It is different, however, with the organic constituents, which have a two-fold source, and of which part, or even the whole, may be derived from the surrounding atmosphere. The atmosphere is, in fact, a great And this is effected partly by tillage, reservoir of the organic constituents of which breaks up the land, and by the adplants, of which it contains all four; two mission of air and moisture facilitates the of these, nitrogen and oxygen, forming al- decompositions, by which these valuable most the whole of it; the other two, carbon constituents of the soil are liberated from and hydrogen, existing in smaller propor- their insoluble state. The other and far tion in the forms, respectively, of carbonic more important means is by the addition to acid and the vapor of water. It must be the soil of those substances which the plant understood, however, that all soils contain requires, in other words by the use of maa certain quantity of the same substances, nures. A manure, then, ought to contain in the form of what is called organic matter, all the substances which a plant requires in a state of which all these four substances for its growth. And this is unquestionably may be supplied to the plant. Now, every what a manure of theoretical composition fertile soil contains all the constituents of should do. Nay, more, it ought to contain the plants which grow upon it, and that, these substances exactly in the proportion too, in sufficient quantity to supply many which the plant requires, so that no waste successive crops, a position which I have may occur. It must, however, be manifest had recently an opportunity of illustrating to every one acquainted with agriculture, in a very complete manner, in a series of and still more manifest to every one acanalyses of the Wheat soils of Scotland, quainted with chemistry, that it is impospublished in the last No. of the Highland sible to carry out practically what is true Society's Transactions. I have there shown in theory; nevertheless, the aim of skilful that even nitrogen, of all others the ele- and scientific practice ought to be to apment which we should least expect to find proach as near to theoretical perfection as in them in abundance, nevertheless exists it is possible to do, though in the very nain what must be considered a comparatively ture of things we cannot even hope absolarge proportion. But it is important to lutely to arrive at it, or even near it. observe that it is not enough that these Although, however, we cannot hope to arsubstances shall exist in the soil; it is fur- rive at perfection, we may advantageously ther necessary that they be present in a aim at a somewhat lower and less difficult state in which they can become available to standard, for experience and science concur the growth of the plant. Now, to provide in showing that all the constituents of a for this, Nature has introduced an ex-manure are not as equally important, but tremely beautiful and important provision. In order that these substances shall be absorbed by the plant, they must exist in a soluble condition. It is, however, very manifest, that if the whole valuable constituents were soluble, the good effects of such an arrangement would be altogether defeated, for the rains would soon wash away from our soils all that they contained of

that those are most essential which the plant has greatest difficulty in obtaining from other sources. Now, in this point of view, nitrogen is the most important of all the constituents of a manure, because it is that which Nature supplies least abundantly. You may possibly express some surprise at this statement, considering that I, not many minutes since, mentioned that