focus of the concave lens should bear to that of the convex lenses the ratio of about 13:8. On the Angular Measurement of the Picture in Painting. The angle subtended by a picture changes as it is removed further from, or brought nearer to, the observer; and by this change in its position the relation of the near objects to the distant ones becomes altered; so that they cannot be equally correct in both positions of the picture. By means of a small instrument, which may be termed the Hand-goniometer, the student is enabled to fix approximately the distances of objects as represented in a picture, especially in subjects where linear perspective is little concerned. The span given to the two arms of the goniometer fixes the proximity of the picture, by assigning a given number of degrees (about 50) to its apparent width, and thus ensures a conformity between the objects there depicted, and the natural subject which they represent. The nearest point of the foreground in a level scene averages about 10 yards from the observer, corresponding to an angle of 10° below the horizon; but when the observer is situated above the general level of the prospect, the picture extends downwards to a greater angle below the horizon, so as to include a larger area, or receding plane, between it and the ground line. Figures would generally appear too large if introduced on the very ground line; the size of the nearest usually corresponds with the proportion of human figures at about 15 yards off, corresponding to about 7° from the horizon downwards. The relation of many other points to the horizontal line may be obtained in a similar manner. A matter of some interest, for marine painters, is the amount of depression of the visible horizon or sea boundary caused by the convexity of the earth; for although a subject of minute inquiry in an artistic point of view, yet it is just sufficiently appreeiable to be worth the artist's consideration; since erroneous drawing, with respect to it, may be observed in many of the pictures of coast scenery; a greater amount of dip of the horizon being accounted for by the concealment of objects behind it, than is consistent with truth. Sir John Herschel, in his 'Outlines of Astronomy,' observes "that two points, each 10 feet above the surface, cease to be visible from each other over still water, and, in average atmospheric circumstances, at a distance of about eight miles;" which limits the horizon of the sea, to an observer's eye situated 10 feet above its level, to a distance of four miles, and assigns to it, at that distance, a real depression of 10 feet only. With the aid of a glass, the effects of so small an amount of depression become easily appreciable on the sea-side. From the shore, at Eastbourne, I could discern only the sails of a large vessel, which may have been ten miles distant; whereas, from an eminence of about 60 feet above low water, I could distinctly see, with the aid of a telescope, the entire hull, which probably rose 15 feet above the water. But a vessel situated at that distance scarcely measures an angle appreciable to the unassisted eye, and therefore becomes too minute an object to be safely represented in a picture, as partially hidden by the sea's boundary line; in fact, this natural effect could only be introduced in very minute art representations. It is true, the extremely foreshortened appearances presented by the sea's surface, to an individual on the beach, causes boats and vessels, stationed at considerable intervals from one another, to appear almost in contact, or to seem on the verge of the horizon, although really not at all remote; but this is owing entirely to the illusions of perspective, and cannot be increased to any appreciable amount by the convexity of the water's surface, or the earth's rotundity. But the case is somewhat different with regard to the amount of depression of the visible horizon, as considered in connexion with the existence of mountains on the coast. The elevation of Beachy Head, amounting I believe to 700 feet above the sea, suffices to cause a depression of the visible horizon, which appeared to me appreciable with the aid of this imperfect instrument; and although this small amount of the horizon's dip does not affect the pictorial character of the sea-view, (which from such a position is remarkable for its vast expanse both horizontally and vertically), yet the convexity of the sea exercises an influence on the outline of very distant mountains which are seen beyond the horizon; for these do not exhibit as they approach the horizontal line any kind of break or change in the direction of their slopes, as is usually observed in the forms of mountains which fall down to the visible edge of the water, but their characteristic curves are cut off, as it were, midway by the line of the horizon which conceals the sea-worn base of each mountain. CHEMISTRY. Address by Dr. LYON PLAYFAIR, F.R.S., President of the Section. My predecessor in this chair, Sir John Herschel, drew our attention to the great importance of studying, with increased accuracy, the combining proportions of bodies in the hope of determining the exact numerical relations which prevail between the elements. He justly regarded it as a subject worthy of the most accurate experiment, to ascertain whether the combining proportion of the Elements are multiples of the combining number of hydrogen, as suggested by Prout; cautioning chemists at the same time not to accept mere approximative accordances as evidence of this relation. I have now to congratulate the Section on the publication of the laborious investigations of Dumas on this important inquiry. It required a chemist of great manipulative skill, as well as of fertile experiment, to obtain combining numbers for the elements upon which a greater reliance could be placed than upon those determined with such admirable precision by Berzelius, that great master of analysis. The atomic weights found by that chemist did not, for many of the simple bodies, confirm the suggestion of Prout as to the multiple relations of these numbers to the equivalent of hydrogen. At the same time the more recent determinations for the atomic weights of Carbon, Silver, and some other elements, so closely coincided with this view, that it was very desirable to extend new experiments to the bodies which had fractional atomic weights assigned to them. In M. Dumas' memoirs there are the results, though not the details, of a large series of experiments on many of the elements. He obtained numbers of precisely the same value as those of the Swedish philosopher when he followed his methods of analysis— numbers which are not the multiple of the equivalent of hydrogen. But when he pursued his experiments upon these same elements, with the new methods of discovery and his own inventiveness, then atomic weights were obtained which corrected themselves from the error inherent in former methods of analysis, and resulted in being multiples of the combining proportions of hydrogen, or in standing in a very simple relation to that number. There is on this point evidence so clear that there is scarcely a chance of deception. The labours of Dumas, Schneider, Marignac, Pierre, Peligot, and others, have established the relation by recent determinations of chlorine, iodine, bromine, silver, titanium, &c.,-elements differing so much in chemical character as well as in atomic weight, that it is difficult to conceive any fortuitous combinations which could have produced such uniformities in the results of analysis. Hence the general view of Prout, that the equivalents of the elements, compared with certain unities, are represented by whole numbers, seems to be established by recent experiment, although it would be premature to declare that there are no exceptions to the law. We are familiar with many ingenious discussions on the natural grouping of the elements, and the relations of their equivalent numbers to each other. I allude to the papers of Gladstone, Odling, and Mercer, and to the views of Cook, in America. Although these efforts point to important dependences of the elements on each other, we cannot yet adopt them as parts of our scientific system. Another question of a different character, as regards equivalents, has recently received attention. I refer to the proposal to double the equivalents of carbon and oxygen, that is, to raise them from 6 and 8, to 12 and 16 respectively. As these two elements are essentially connected with the whole system of chemistry, the right determination of their equivalents is a matter of extreme importance. Undoubtedly there are cogent reasons which induce many of our able chemists 1859. 5 to double the equivalents of carbon and oxygen, and they are well worthy of the calm and deliberate consideration of a meeting like this. Such an alteration would produce an immense change in the literature of the science, and should only be adopted if the benefit to be derived from it proved to be so great as to justify the inconvenience. This subject will be brought before the Section on more than one occasion. The change proposed has, in a great measure, resulted from the new views of the classification of organic compounds introduced by Gerhardt. The recent brilliant progress in organic chemistry has resulted in the discovery of a vast number of new compounds. A scheme of classification became urgently necessary for them, and the genius of that great French chemist produced a system which has exerted a most important influence on the advancement of science. The comprehensive system planted by Gerhardt has been carefully watered and tended by our countrymen Williamson, Hunt, Odling, and Brodieuntil the young plant has attained a most vigorous growth. In a report upon the state of organic chemistry, by one of these gentlemen, we shall have the advantage of tracing its effect on the advance of science. Another of our members who admires the beauty of the plant, and the excellence of the fruit it has borne, fears that it is growing too wildly, and that the pruning-knife might be adopted with advantage, He therefore proposes for our consideration, in a paper which will be laid before you, some modifications of the system of classifying compounds now so prevalent. With the array of talent in our Section, enlisted in favour of Gerhardt's system, there will be full justice rendered to the merits of that lamented philosopher in any discussion which may follow the reading of the paper to which I allude. In conclusion, I have to congratulate the Meeting upon the important muster of English chemists in our Section; although we have at the same time to regret that our cold northern position has prevented our foreign colleagues from joining us, and enjoying that welcome which the warm hearts of our countrymen would assuredly have accorded to them. On the Solubility of Bone-earth from various Sources in Solutions of Chloride of Ammonium and Common Salt, By Mr. BINNEY. On Pentethyl-stibene. By G. B. BUCKTON, F.R.S., F.C.S. This paper detailed the preparation of a new organo-metal compounded of one equivalent of antimony and five of ethyl. The author stated that great difficulties presented themselves in isolating the new body, from the tendency it showed to split by distillation into ethyl and triethyl-stibene. In this decomposition it imitates the deportment of pentachloride of antimony, which by heat evolves chlorine. The existence of this substance, the author conceived, had some importance, since it confirmed the views lately advanced by some chemists, that the ethyl compounds of antimony and of arsenic form no exceptional cases, but are most naturally referred to the types of antimonious and antimonic acids, &c. On the Specific Gravities of Alloys. By F. CRACE CALVERT, Ph.D., F.R.Š., F.C.S. &c., and RICHARD JOHNSON, F.C.S. &c. The study of alloys and amalgams having been made especially with impure or commercial metals, the results obtained haye been such that it has been impossible to solve the important question, Are alloys and amalgams chemical mixtures or compounds? It is with the hope of throwing some light on this subject that we have for the last two years been engaged in examining, comparatively, some of the physical properties, such as the conductibility of heat, tenacity, hardness, and expansion of alloys and amalgams made with pure metals, and in multiple and equivalent quantities as follows: 1 Copper and 1 Tin 1 Tin and 2 Copper 1 "" 2 3 and 4 1 " 4 By this method we have succeeded in ascertaining, first, the influence which each additional quantity of a metal exerts on another; secondly, the alloys which are com pounds and those which are simple mixtures; for compounds have special and characteristic properties, whilst mixtures participate in the properties of the bodies composing them. This method of investigating alloys and amalgams has enabled us to ascertain the metals which combine together to form definite compounds, and those which, when melted together, only form mixtures. Thus, for example, bronze alloys are definite compounds, for each alloy has a special conductibility of heat. Thus the alloyObtained. Calculated*. Difference. These same alloys have a specific gravity of their own. Thus The same fact is also observed in the expansion or contraction of these alloys i whilst, on the contrary, the alloys of tin and zinc being mixtures, conduct heat, have a specific gravity, and expand according to theory, or the proportion of tin and zinc which they contain. Thus for heat The authors then gave tables showing the specific gravity of various alloys and amalgams divided under two heads : ·-- I. Those which have a higher specific gravity than indicated by theory. Of this class there were five series, viz. copper and tin, copper and zinc, copper and bismuth, copper and antimony, and tin and zinc,—comprising thirty-one alloys. II. Those which have a less specific gravity, or expand. Of these there are six series, viz. mercury and tin, mercury and bismuth, mercury and zinc, antimony and bismuth, bismuth and zinc, and tin and lead,-comprising forty alloys and amalgams. Their researches reveal two important facts; first, that there is one metal the alloys of which always contract, viz. those of copper, whilst all the amalgams expand or have a less specific gravity; secondly, that the maximum expansion or contraction of alloys and amalgams generally occurs in those which are composed of one equivalent of each metal, the exception being those of tin and zinc. But this arises no doubt from the fact, that all the alloys, with the exception of the latter, are compounds and not mixtures. In conclusion, attention is drawn to the extraordinary contraction or expansion that some of these alloys experience. Thus, for example, the alloy of three of copper and one of tin, Found. Calculated. Difference. whilst the amalgams of tin expand to nearly the same extent, as shown by these results: *The principle upon which the theoretical conductibility, specific gravity, and expansion are calculated, is similar to that followed with respect to hardness, for which, see Philosophical Transactions, 1858. On the different Points of Fusion to be observed in the Constituents of Granite. By M. F. BIALLOBLOTZKY. On the Formation of Rosolate of Lime on Cotton Fabrics in Hot Climates. By F. CRACE CALVERT, Ph.D., F.R.S., F.C.S. The author exhibited some pieces of calico which were covered with red stains, and he stated that a short time previously the cargoes of two ships on arrival in India had been found to be extensively damaged by these stains. After a great number of experiments he had found those stains to be due to rosolate of lime, the formation of which he traced to the following cause. Amongst the packing or materials used to surround the bales and protect them from wet and injury, was a kind of waterproof felt made of corded cotton bound together and strengthened by a layer of gutta percha which had been dissolved in impure coal naphtha, the cloth thus made having been then pressed between cylinders. Under the influence of the warm and damp atmosphere of India, the hydrate of oxide of phenyle, or carbolic acid, became volatilized, and coming in contact with the carbonate of lime contained in the calico, was transformed into rosolate of lime. The correctness of this result was proved by enclosing pieces of white calico in bottles with pieces of the felt, the calico being uppermost; and also by placing a little carbolic acid at the bottom of the bottles instead of the felt, the bottles being kept at a temperature of 110° Fahr. for several days, when in both instances the calico exhibited red stains identical with those which he had previously found in the goods returned from India. On Crystallized Bichromate of Strontia. By Dr. Dalzell. On the Economical Preparation of Pure Chromic Acid. Dr. Dalzell having experimented on large quantities of material, recommends as the result of his investigation, the process of Traube for the production of the impure acid and its perfect purification by from four to seven recrystallizations, and compression of the products between large porous tiles. He describes the modifications in colour and density which chromic acid presents, according to the process by which it has been prepared. Before applying the baryta test for its purity, Dr. Dalzell reduces with alcohol and nitric, not hydrochloric acid; and he states that when the solution of sesquioxide was diluted, twelve hours at least should be allowed for the action of the test before the purity of the product was affirmed. Dr. Dalzell also proposes bichromate of strontia as a means of obtaining pure chromic acid. He gave the particulars of the process for obtaining the strontia salt of absolute purity from carbonate of strontia and commercial chromic acid. Bichromate of strontia crystallizes with three atoms of water, all of which it loses at 212° Fahr. He has obtained from it pure crystallized neutral and acid chromates of many of the metals by employing equivalents of their soluble sulphates. Dr. Dalzell gave the particulars of the composition of several of the metallic chromates; and referring to the action of bichromate of potash on a solution of chloride of barium, stated that when the temperature of the liquid is raised to the boiling-point, Peligot's salt is abundantly formed. He recommends this as the best method for preparing the bichromate of the chloride of potassium. The author stated that he was at present engaged in further researches on the crystallized chromates. Dr. DAUBENY exhibited specimens of several varieties of Volcanic Tufa from the neighbourhood of Rome and Naples. Reports from the Laboratory at Marburg. By Dr. GUTHRIE. |