The author next described the problem of determining the true wind from the observed motion of the vessel and the apparent wind, as being merely a special instance of the general theorem of the parallelogram of forces, the course of the ship being one side; the apparent wind, the diagonal; and the true wind, another side; so that the case might always be reduced to the calculation, according to the usual rules for plane triangles, of the third side and one of the angles of a triangle, from the two other sides of their included angle, excepting in the simpler conditions of going exactly with or against the wind. But as the calculations in this way, though easy enough, threatened to be uselessly and overpoweringly burdensome, considering the enormous number of cases which would have to be computed in any voyage, the small degree of accuracy required, and the untoward nature, for trigonometrical calculations, of the data as observed for the ordinary purposes of navigation, the author contrived a simple set of scales, in which, entering with the directions and velocities of the ship and apparent wind, as usually observed, the direction and velocity of the true wind are given at once by inspection; and might be inserted, with very little trouble to naval officers, in two appropriate columns introduced into the log-books, as kept at present. The following Donations to the Library were announced :— First Report on the Coals suited to the Steam Navy. By Sir Henry De la Beche and Dr Lyon Playfair. 8vo.-By Sir Henry De la Beche. The American Journal of Science and Arts. Conducted by Professors Silliman and Dana. Second Series. January 1848, No. 13. 8vo.-By the Editor. Bouet-Villaumez (Le Comte E.) Description Nautique de l'Afrique Petit-Thouars (Abel du). Voyage auteur du Monde sur la Frégate Imp. Fol. (In sheets.) Marins. Exposé des Opérations Géodésiques. 1839. Beyat. Le même. 1844. 4to. 8vo. 4to. Jehenne (M.) Renseignements Nautiques sur Nossi-Bé, NossiMitsiou, Bavatoubé, &c. 8vo. Urville (J. Dumont d') Voyage au Pole sud, et dans l'Océanie, sur les Corvettes L'Astrolabe et la Zelée. 8vo. Daussy (M.) Nouvelle Méthode pour calculer la Marche des Table des Positions Géographiques des principaux lieux du 8vo. Brossay (M. Chiron du). Instructions Nautiques sur l'Attérrage et 8vo. Jehenne (M.) Renseignements Nautiques sur l'Ile Mayotte. 8vo. Spittal (Robert), M.D., Introductory Discourse on Pathology and the Practice of Medicine. 12mo. By the Author. Journal of the Statistical Society of London. Vol. II. Part 1. March 1848. 8vo.-By the Society. Monday, 17th April 1848. DR CHRISTISON, V.P., in the Chair. The following Communications were read: 1. On the Action of the Dry Gases on Organic Colouring Matters, and its relation to the Theory of Bleaching. By Dr George Wilson. This communication is divided into six sections. In the first, the author states that the object of his paper is to supply a defect in the theory of chlorine-bleaching, by endeavouring to explain why the removal of water from that gas arrests its bleaching action. In the preliminary discussion, he refers at some length to Davy's theory, that moist chlorine does not bleach directly, but only in a secondary way, by combining with the hydrogen of the associated water, and liberating the oxygen, which is the true bleacher. After pointing out the untenable assumptions and self-destructive arguments on which this theory is built, the author proceeds in the second section, which discusses the influence of sunlight on the bleaching action of dry chlorine, to shew, that Davy's proposition that dry chlorine does not bleach dry organic colours is true, provided direct sunlight be excluded, but does not apply to the gas when exposed to the actinic influence of the sunbeam. In a comparative trial, one specimen of dry litmus paper was found to resist the decolorizing action of dry chlorine for more than eight months when kept in darkness; whilst the colour of another portion of the same paper totally disappeared after six weeks' exposure to sunshine. Another comparative experiment was not so successful as regarded rapidity of actinic bleaching; but both sets of trials led the author to infer, that darkness as well as dryness is essential to the negative action of chlorine on colours. The third section is occupied with the record of experiments, instituted with a view to determine whether the presence of water is as essential to the bleaching action of oxygen, sulphurous acid, and sulphuretted hydrogen, as it is to that of chlorine. The general result of the trials made was, that the gases mentioned may be retained, when dry, for months over dry litmus, without decolorizing it; and that they are, therefore, at least as much dependent as chlorine on water for their power of bleaching. The fourth section investigates, in like manner, the extent to which the acid gases and ammonia have their power to change organic colouring matters, influenced by the absence of water from the gas and the colour. The author finds that the modifying action of carbonic, sulphurous, and hydrosulphuric acids on colours, is totally arrested by the abstraction of water; and that that of hydrochloric acid and ammonia is long delayed. He infers, from the results detailed in sections third and fourth, that there is nothing exceptional or anomalous in the non-bleaching action of dry chlorine, and that it is only a particular case of a general law, applying to all gases which affect colours, and teaching that elastic fluids, when anhydrous, lose in whole, or in part, the power to destroy or change the tints of organic bodies, which they possess when associated with water. Section fifth reviews the methods employed for drying gases, and the tests of gaseous dryness. It enters at length into the question, how far it is possible to confer absolute dryness on an elastic fluid, and suggests some modifications of the processes at present in use, which the author thinks will prove serviceable. Non-action on colouring matter is likewise pointed out as a negative test of dryness of some value, in relation to the gases which act on colours. Section sixth is devoted to the question, Does water accelerate the action of gases on colours, in virtue simply of its conferring mediate liquidity on the gas ? The author thinks not, and refers to the slow action which he has observed of liquid anhydrous bromine and sulphurous acid on blue litmus, as contrasted with their rapid production of destruction or modification of colour when dissolved in water, as shewing that the liquefaction of the gas is not the only cause of its rapid action when moist. He contends that this is only to be fully accounted for by taking into consideration the power of water to liquefy both the colouring matter and the gas, and thus to bring them into a closeness of physical contact in the highest degree favourable to energetic chemical action. The author was led, in connection with this view, to infer that dry gases would act on dry colours in other liquids besides water, provided only these could dissolve both the gas and the colouring matter. He finds, however, that this cannot be laid down as a general proposition, at least so far as chlorine is concerned, the only gas on which he has had opportunity to make researches in reference to this point. The volatile oils of the type of spirit of turpentine (C 5, H 4) and chloroform, which contain no oxygen, and sulphuret of carbon, which contains neither of the elements of water, dissolve the colouring principle of alkanet root, and also chlorine, but the gas does not destroy the colour. Solutions of dry litmus, on the other hand, in chloroform and sulphuret of carbon, are instantly bleached by dry chlorine. The author's final conclusion is, that the function of water in bleaching, speaking generally, is to dissolve the colour and the gas, and so to bring them within the sphere of chemical affinity; and that water is more efficacious in accelerating bleaching than other liquids, simply because it excels most of them in solvent power. 2. On the Products of the Destructive Distillation of Animal Substances, Part I. By Dr Thomas Anderson. In this communication the author details the general properties of bone-oil, the substance employed in his experiments, and those of certain of the volatile bases contained in it. The oil was first rectified, and the product collected in two separate portions, each of which was separately agitated with dilute sulphuric acid for the separation of the bases. The acid solution so obtained was then boiled down to a small bulk for the purpose of separating any non-basic oil which might have been dissolved, and distilled with potash, soda, or slaked lime. The bases passed over in solution in water, from which they were separated by means of solid caustic potass; similar processes were performed with both portions of the bone-oil, but in the present paper the author confines himself to the pure volatile portion only. The oil separated by this process from the more volatile portion was found to be a mixture of at least four or five different bases, which were separated from cach other by fractionated distillation. The most volatile of these, which boils at about 175° Fahr,, was present in extremely minute quantity only. For it the author proposes the name of petinine (from Teremos, volatile.) It is a transparent colourless fluid, highly soluble in water, alcohol, and ether. The smell is pungent, and resembles that of ammonia, but is accompanied by the odour of decaying apples. It gives, with chloride of gold, a pale-yellow precipitate, and with bichloride of platinum and corrosive sublimate, beautiful crystallisable salts, the former resembling iodide of lead, the latter in pearly plates. The analysis of petinine gave results corresponding with the formula C, H, N, which was confirmed by the constitution of the platinine salt, the formula of which was found to be C H10 N, H Cl, Pt. Cl. The author details, as far as the minute quantity at his disposal would allow, the properties of the salts of this base. 10 He then takes up the consideration of that portion of the mixed basis, which distilled between 270° and 280°, which, after successive rectifications, was found to give the formula C12 H, N, and to agree in all its properties with the base formerly obtained by the author from coal-tar, and described under the name of picoline. Aniline 12 |