Glass and india rubber. Exp. 5. In a piece of brass similar to the above, fig. Exp. 5. A, instead of sealing wax, I placed a piece of Caoutchouc, or indian rubber of the same shape as the wax. This body produced here a singular phenomenon (observed in other cases) which characterizes the manner in which friction acts in these phenomena; its effects changing, according to circumstances foreign to the intrinsic nature of bodies. This experiment is difficult, on account of the tendency of the indian rubber to stick to the glass cylinder, by which the former is torn or disfigured if the pressure is too great, or the motion too rapid: it is therefore necessary to find the proper degree of both. Now, according to these (or other unperceived circumstances) having repeated this experiment on different days, sometimes the glass took off some electric fluid from the indian rubber, and made the electroscope 11 diverge positively; at other times it was the reverse; and in both cases the indian rubber was in the state opposite to that of the glass cylinder, as shown by the electroscope 19. Exp. 6. It has been seen in exp. 1, that a brass rubber, Exp. 6. applied to the glass cylinder, becomes negative, the latter Brass and sealing wax. becoming positive. I covered a similar glass cylinder with a thick coating of sealing wax, and applied to it a brass rubber of the same breadth as the former, fitted to the sealing wax cylinder: it produced no sensible effect. I suspected, that this rubber was too wide: because thus embracing, in a great length, half the circumference of the sealing war cylinder, which constantly revolved against it, the sealing wax lost and regained alternately electric fluid on too great a surface; for the point 12, with which communicates the prime conductor, to preserve any sensible change. With this idea, I reduced the breadth of the brass rubber, in the part bearing on the sealing war, to of an inch; placing the point 12 of the prime conductor, immediately under and very near the extremity of the rubber. Then the electroscope 11, communicating with the rubbed sealing wax, diverged negatively, and the electroscope 19, communicating with the brass rubber, diverged positively. This experiment shows, in the first place, the errour of Distinction of a distinction between bodies as electrics and anelectrics electrics per se (electric improper. Nether are there two tricity. (electric per se, and electric by communication, as they have been also called); considering friction as the test between these two classes of bodies, and placing metals foremost among the anelectrics. But it is seen in the above experiments, that there is no such distinction, since brass undergoes, by friction, changes in its electric state, as well as resinous bodies and glass: only these changes, in conducting bodies, cannot be manifested without insulation; and the want of this condition in the experiments of former electricians was the cause of the errour. The same experiments show also, that brass (as a metal) kinds of elec- becomes either positive or negative, according to the body with which it undergoes friction. In the above experiment the brass rubber was made positive, because it took off some electric fluid from sealing-war; but in exper. 1 it was made negative, because it lost some of the fluid to glass. But this difference in the electric state of the same body, by the difference of those with which it undergoes friction, extends farther; and the following experiment will show the errour of the distinction between two electricities, in which one is called resinous and the other vitreous; and in general between two fluids, or two electric properties in different bodies. Exper. 7. Sealing wax and india rubber. Exper. 7. It has been seen in the last experiment, that the sealing-wax cylinder was made negative, by being rubbed with brass. To the same cylinder I applied the indian rubber; and with the smallest pressure (to prevent adhesion), and a very slow motion of the winch, the gold leaves struck so rapidly in both electroscopes, that, in order to try the kinds of divergences produced, I was obliged to stop at one part only of a revolution: then I found constantly, that the sealing-wax, which in the above experiment was rendered negative by brass, now became positive; and that the indian rubber, which in exper. 5 became sometimes positive with the glass cylinder, was here constantly negative. Therefore sealing-wax itself either loses or gains some electric fluid, according to the body which exercises friction upon it, and the rubbing bodies always experience the contrary effect. tive. I have made various experiments of the same kind, with Farther proof various bodies, all affording the same general result; but I of a body becoming possi shall only relate one more, giving another example of a tive or nega body which becomes either positive or negative according to the other body with which it undergoes friction. This is one of the beads, of the size and colour of cherries, worn by indian women, which, as Dr. Lind informs me, consist of an inspissated vegetable oil: they are not soluble by water, and are very elastic. Exper. 8. I mounted one of these beads on a spindle, as Exp. 8. in fig. B. The bead, 1, is traversed by a small glass axis, 2, 2, covered with sealing-wax, to the ends of which are adapted pieces of wood, 3 and 4, on the first of which is seen, at 5, the ridge before mentioned, which prevents the spindles from coming out when placed between the pillars of ́the apparatus. 1. With a narrow brass rubber, the extremity of which is fitted to the form of the bead, the slowest motion of the winch renders the bead negative, and the brass rubber positive. 2. With a sealing-wax rubber like that fig. A, but fitted to the form of the bead, with very little pressure and motion, the bead becomes positive, and the sealing-wax negative. disturbs the equilibrium of Such are the constant phenomena observed at the foun- Friction only tain head of all the electric effects, which it is in our power to produce; and they depend on friction, respecting which the electric various systems have been fabricated. Now from the whole fluid; tenour of these experiments it may be laid down as a fundamental truth in terrestrial physics, that friction has no Other influence in electric phenomena, than that of disturbing the equilibrium of the electric fluid, in such a manner, that one body, by acquiring a certain quantity of it above what it had before, is rendered positive, and that the other is found negative, as having lost that quantity. It is only and it is then when its equilibrium is disturbed, that the electric fluid is alone manifest manifested to us: the electroscope is our first test of this disturbance; but if the bodies, either conductors themselves, or associated with conductors, are of a sufficient ize, and the electic difference between them has arrived to a certain to us. a certain degree, it is manifested by a spark darting from one to the other, and the equilibrium is thus restored. I cannot but consider the fixation of this point, after many controversies, as being no less conducive to the advance of our knowledge in the maze of terrestrial causes, than the determinations conceruing air and the cause of heat; and no experiments and observations appear to me to deserve more the joint endeavours of experimental philosophers, than those concerning the modifications of the electric fluid, in the atmosphere and in the ground, of which, in my former paper, I have shown the great influ ence in terrestrial phenomena. Ashfield, near Honiton, 12th October, 1810. Lime in the immediate principles of vegetables. What becomes II. Comparative Examination of the Mucous Acid formed by the MR. R. VAUQUELIN, by his experiments on gums arabic and tragacanth, has ascertained the existence of a considerable portion of lime in the immediate principles of vegetables. The reading of his paper suggested to me the following reflexions. 1st, What becomes of the lime contained in these gums,. of this in con- when they are treated with nitric acid, in order to obtain verting gums into mucous the mucous acid? acid? 2dly, Does it not combine with the oxalic acid, which is formed almost at the same time as the mucous ? 3dly, As the oxalate of lime is more insoluble in water than the mucous acid, does it not fall down with this acid when the residuum of the process is washed, and occasion a sensible alteration of its properties? 4thly, How may we ascertain the presence of oxalate of lime in the mucous acid obtained from gums, and separate this calcareous salt from the acid, the purity of which it affects? * Abridged from the Annal. de Chim. vol. LXXII, p.81. T. To solve these questions I undertook the following expe- Experiments riments. to find this. canth con I digested 60 gram. [926-4 grs.] of gum tragacanth in Gum tragaeight times their weight of pure nitric acid at 36° [sp. grav. verted into 1333]; heated the mixture, till it was reduced to the mucous acid, consistence of honey; and then added a sufficient quantity of water. This would not dissolve a white, pulverulent substance, which, collected on a filter and dried in the open air, weighed 9-5 gram. [146-7 grs]. This was mucous acid. The liquid containing the soluble portion of the mixture was of a yellow colour. I evaporated it, till the moment I perceived a slight pellicle form on its surface, when I removed it from the fire. As it cooled, it deposited a great quantity of crystals, some in laminae, others in needles. easily perceived to be oxalic acid. To separate this acid Oxalic acid. also formed, from the mucous, I poured on the mixture alcohol at 40° [sp. grav. 0.817], which dissolved the oxalic acid, without acting on the mucous. This, collected on a filter, weighed 2.1 gram. [32.4 grs]. The alcoholic solution, being gently evaporated, yielded a coloured mass, which I dissolved in water to obtain whiter and purer crystals. The mother waters of this second portion of mucous and malic. acid and of oxalic acid contained a mixture of oxalic and malic acids, which I separated by means I shall not men tion, as they are foreign to my subject. acid The first portion of mucous acid I obtained was very The mucous white. When dried it had the clotted appearance of starch. This I employed in my experiments, rejecting the second portion, which did not appear to ine so pure. oxalate of lime. To find whether there were any oxalate of lime in this contained mucous acid, I mixed one part of the nitric acid abovementioned with teu of distilled water, and poured it on the mucous acid. I then exposed the whole to a heat of 40° or 50° [104° or 122° F.] for 48 hours, shaking it occasionally, to promote the action of the menstruum. The supernatant liquor being poured off, ammonia immediately threw down from it a white earthy salt in silky filaments, which had all the physical properties of oxalate of lime. A second |