and beautiful, skirting a lofty ridge of mountains running from west to east, but at some distance from the base. At length arrived at a vast enclosure resembling an English park, kept up for the breeding of horses. It is considered half-way. Found an empty house, or rather shed, where we breakfasted, turning our horses out to graze, secured by a long rope. Rested in this enchanting spot for about an hour and a half, and then proceeded. The road more rocky and uneven, and the soil less fertile; passed a house pleasantly situated on a little hill, with a garden and tobacco ground attached; it was occupied by a negro, who seemed happy in his hermitage. Entered a savanna skirted by wood, and said to abound in jaguars: had not gone far before we started a species of racoon, who afforded capital sport, but being myself in the rear, the mules were not active enough to stop him, and he escaped wounded into the bushes. Soan started another racoon; took the lead and drove him into a small thicket where we surrounded him, and fired three shots, two of which hit him before he would start. The animal we killed is called a wild dog, which he resembled much, but his head was like a fox's; skin spotted like the leopard, but good for nothing, being mangy. The land higher as we advanced and more undulating. Soil still rich in many places. Approaching Palmar the grass was on fire: this is the Spanish method of clearing the land, and doubtless tends to impoverish it, but makes the herbage in the plains sweet and excellent for cattle. At three P.M., reached that pretty little mission, the best laid out we had yet seen.— [The conclusion of this journal, with a map of the traveller's route, will be given in our next Number.] ART. XI. On a Substance produced during the Distillation of Coal Tar. By W. T. BRANDE, Sec. R.S., Prof. Chem. R. I., &c. SOME years ago I received from Mr. Clegg, engineer to the Gas Light and Coke Company, a small quantity of a brilliant white crystalline substance, which I was informed was benzoic acid; and that it had been found in the condensing vessel of the coal-gas apparatus. I then paid no further attention to it than slightly to examine its properties, and finding it not acid, and insoluble in liquid ammonia, merely concluded that it was not what it had been represented. Very lately, I am indebted to Mr. Jennings for a large supply of what I consider to be the same product; he informs me that it is produced in considerable quantities in the first and second distillation of coal tar; that it gradually precipitates from the oil, and that every hundred gallons deposit about five pounds of it; that the deposition is greatest in cold weather; and that it is consequently probable that the oil, even when highly reetified, retains a portion of it in solution. The substance, when freed from empyreumatic oil, is inodorous and insipid; it is extremely volatile, and fusible at a temperature a little below that of boiling water. Its vapour condenses in brilliant needles, and plates; the latter appearing hexaëdral, and often perfectly transparent. After fusion, it concretes with much expansion, on cooling, into a soft fibrous crystalline mass, of a specific gravity little exceeding that of water. It is highly inflammable, and during combustion throws off a very remarkable quantity of carbonaceous matter. It is insoluble in water. Alcohol sp. gr. 820, readily dissolves this substance, and acquires an acrid and aromatic flavour. The solution is decomposed by water, and a milky mixture results. Hot alcohol appears to dissolve it in any quantity; and as the solution cools, it is deposited in beautiful crystalline flakes. Sulphuric ether, at common temperature, also dissolves it in large quantities; and fine crystals are separated during the spontaneous evaporation of the solvent. In chlorine, this substance fuses spontaneously, and evolves fumes of muriatic acid; the gas is absorbed with the production of heat, and a compound results, apparently analogous to that obtained by the mutual action of chlorine and olefiant gas. Intensely heated in chlorine, it deposits charcoal, but does not burn. It dissolves in acetic acid, and is not much more soluble in the hot, than in the cold acid. Muriatic acid scarcely dissolves it. In sulphuric acid, when aided by heat, it dissolves in considerable abundance, forming a deep violet-coloured solution, which bears diluting with water without decomposition. The alcalies produce in this solution a white flaky precipitate, and if diluted, the mixture becomes curiously opalescent, in consequence of the separation of numerous small flakes. By long-continued boiling with sulphuric acid, a portion of carbon is deposited; but the greater part of the substance volatilizes unaltered. Repeatedly distilled with nitric acid, this substance appears to suffer scarcely any change; a portion is retained in solution, by the acid, which is precipitated by dilution, and another portion passes over unaltered. In the caustic and carbonated alkalis, it is scarcely soluble. This substance appears to suffer no change whatever by repeated sublimations, at temperatures above that of boiling water; and what is more curious, is, that its vapour may be passed through a red hot tube without decomposition; if received into a cool glass globe, it crystallizes in white plates as before. Fused with potassium, it scarcely acts upon that metal; and as the mixture cools, it oozes from it in brilliant globules. Such are the few experiments which I have hitherto been able to make upon this peculiar product. It bears in appearance so strong a resemblance to the fatty matter of biliary calculi, that I was once induced to consider it nearly of the same nature; but, as Dr. Wollaston remarked to me, it is not only much less fusible, but considerably less volatile, than that compound, and perhaps approaches, in most respects, nearer to the properties of camphor, than of any other known body; though, as the above experiments tend to shew, it exhibits several peculiarities. Its remarkable indestructibility by heat; the circumstance of its neither affording water nor carbonic acid, when heated in close vessels, and its very trifling action upon potassium, are circumstances which induce me to believe that it contains no oxygen; and which, in conjunction with the effects produced upon it by chlorine, lead me, for the present, to regard it as a binary compound of carbon and hydrogen: in respect to the proportions, however, in which these elements are combined, I have not yet as been able to satisfy myself. Upon another occasion I hope to give some further details respecting the above product; and to examine another substance, which Mr. Jennings informs me he has obtained during the rectification of coal tar. Royal Institution, ART. XII. On M. CARNOT's Theory of Defence by Vertical Fire. M. CARNOT, influenced probably by motives which it is not our business to expound or inquire into, has promulgated some singular doctrines respecting the defence of fortified places by vertical fire, a system which has long been acknowledged as furnishing an important accessory mean; but not, we believe, till M. Carnot's proposal, ever thought of as the basis of defence. Sir Howard Douglas has published a small tract, entitled, "Observations on the Motives, Errors, and Tendency, of M. Carnot's Principles of Defence," which has furnished us with the following paragraphs; and which may serve to remove the erroneous impressions, which authority so high as that of M. Carnot might otherwise produce. M. Carnot recommends, that the besieged should begin to make use of vertical fire upon the commencement of the construction of the third parallel; and from that stage of the siege, keep up an incessant discharge of musketry and four-ounce iron balls, at great elevation, upon the enemy's works, so as to form a rain (pluie) of shot upon the trenches. The iron balls to be discharged from a number of 12-inch mortars, two of which are placed in the salients of each bastion and ravelin, in the front, or fronts, attacked; each mortar throwing 600 balls at every discharge. M. Carnot introduces his theory of the effect of these balls by observing, that of any number which fall in the trenches, the number that take effect will depend upon the proportion which the unoccupied part of the trench bears to the part which is covered by the men posted and working in it. Thus, supposing a man standing upon an horizontal plane, to cover a space of about a foot square, and a man in the attitude of working somewhat more, M. Carnot calculates that the projections of the bodies of the men, usually working and posted in the trenches, will occupy about part of their surface; from which he infers, that of every 180 balls that fall in the trench, one should, according to the doctrine of chances, hit a man; and he does not doubt that it will put him " hors de combat." M. Carnot's idea of the effect of this "pluie de balles," is founded upon the velocities which he supposes they will acquire in accelerated descent from the vertex of a very elevated curve. This is manifestly the principle upon which he tries to establish his theory; and this it is which, disregarding for the present the doctrine of chances, Sir Howard Douglas first remarks upon. "It is quite clear," says he, "that M. Carnot has formed his theory upon the parabolic hypothesis, which is the theory of a projectile's flight in a non-resisting medium. This theory, considerably erroneous in all cases, is particularly and greatly so with small projectiles; and its deductions, as applied to the velocity of descent of small balls used in very elevated short ranges, are quite fallacious. The velocity of the ball in a horizontal direction (which by this theory would be constant, and to the projectile velocity, as radius to the cosine of the angle of elevation), being inconsiderable, it is evident that the effect of vertical fire must depend upon the velocity of descent in the direction of the curve. Estimating this according to the parabolic theory (as the secant of the angle of elevation), the motion would be slowest at the vertex of the curve, and the velocities of the projectile be equal at equal distances from that point. According to this supposition, we should assign to the descent |