The mean is 140.17 from 100 of silver. If we suppose 100 of silver to form 107.5 of oxide, we shall have Oxide of silver Acid of arsenic 107.50 Consequently 1 of acid of arsenic will produce 4.29 of arseniate of silver; 1 of white oxide of arsenic, 4.97; and 1 of arsenic, 6.56. Of Mercury. All the oxides and saline compounds of mercury laid in a drop of marine acid on gold with a bit of tin, quickly amalgamate the gold. A particle of corrosive sublimate, or a drop of a solution of it, may be thus tried. The addition of marine acid is not required in this case. Quantities of mercury may be rendered evident in this way which could not be so by any other means. This method will exhibit the mercury in cinnabar. It must be previously boiled with sulphuric acid in the platina spoon to convert it into sulphate. Cinnabar heated in solution of potash on gold amalgamates it. A most minute quantity of metallic mercury may be discovered in a powder by placing it in nitric acid on gold, drying, and adding muriatic acid and tin. A trial I made to discover mercury in common salt by the present method was not successful, owing, perhaps, to the smallness of the quantity, which I employed. I am, sir, yours, &c., JAMES SMITHSON. SOME IMPROVEMENTS OF LAMPS. From Thomson's Annals of Philosophy, Vol. XX; New Series, Vol. IV, 1822, p. 363. SIR It is, I think, to be regretted, that those who cultivate science frequently withhold improvements in their apparatus and processes, from which they themselves derive advantage, owing to their not deeming them of sufficient magnitude for publication. When the sole view is to further a pursuit of whose importance to mankind a conviction exists, all that can do so should be imparted, however small may appear the merit which attaches to it. Of the Wicks of Lamps.—The great length of wick commonly put to lamps for the purpose of supplying the part which combustion destroys, is, on several accounts, extremely inconvenient. It occupies much space in the vessel, and requires an enlargement of its capacity; it is frequently the occasion of much dirt, &c. This great length of wick is totally unnecessary. It is advantageously supplied by a tube containing a bit of cotton wick about its own length, or some cotton wool, fig. 1, and at the end of which is placed a stout bit of wick or cotton wool, fig. 2. This loose end receives a supply of oil from the cotton under it with which it is put into contact, and when it becomes burned, it is easily renewed. A loose ring of wick may in like manner be applied to the argand lamp. This removes the necessity of the long tube into which the wicks, now used, descend, and thus greatly contracts this lamp in height. Of Wax Lamps.-Oil is a disagreeable combustible for small experimental purposes, and more especially when lamps are to be carried in travelling. I have, therefore, substituted wax for it. I experienced, however, at first, some difficulty in accomplishing my object. The wicks of my lamps are a single cotton thread, waxed by drawing through melted wax. This wick is placed in a burner made of a bit of tinned iron sheet, cut like fig. 3, and the two parts a a raised into fig. 4. This burner is placed in a china cup, about 1.65 inches in diameter, and 0.6 in. deep. Fragments of wax are pressed into this cup. But great care must be taken that each time the lamp is lighted, bits of wax are heaped up in contact with the wick, so that the flame shall immediately obtain a supply of melted wax. This is the great secret on which the burning of wax lamps depends. When the wick is consumed, the wax must be pierced with a large pin down to the burner, and a fresh bit of waxed cotton introduced. I employ a wax lamp for the blowpipe. This has, of course, a much larger wick, and this wick has a detached end to it, as above described. Extinguishing Lamps.-The best way of doing this is to extinguish the ignited part of the wick by putting sound wax on to it, and then blowing the flame out. This preserves the wick entire for future lighting again. This mode applied to candles is much preferable to the use of an extinguisher, or douters, to which there are many objections. ON THE CRYSTALLINE FORM OF ICE. From Thomson's Annals of Philosophy, Vol. XXI; New Series, Vol. V, 1823, page 340. March 4, 1823. SIR: I have just seen a memoir in the Annales de Chimie et de Physique for Oct. 1822, but published about a month ago, on the crystalline form of ice. Mr. Hericart de Thury is said to have observed ice in hexagonal and triangular prisms; and Dr. Clarke, of Cambridge, in rhomboides of 120° and 60°. M. Haüy supposed the form to be octahedral, and so did Romé de l'Isle; and, if I mistake not much, there is in an ancient volume of the Journal de Physique by Rozier, an account of ice in acute octahedrals. Are these accounts and opinions accurate? Hail is always crystals of ice more or less regular. When they are sufficiently so to allow their form to be ascertained, and which is generally the case, it is constantly, as far as I have observed, that of two hexagonal pyramids joined base to base, similar to that of the crystals of oxide of silicium or quartz, and of sulphate of potassium. One of the pyramids is truncated, which leads to the idea that ice becomes electrified on a variation of its temperature, like tourmaline, silicate of zinc, &c. I do not think that I have measured the inclination of the faces more than once. The two pyramids appeared to form by their junction an angle of about 80 degrees. Snow presents in fact the same form as hail, but imperfect. Its flakes are skeletons of the crystals, having the greatest analogy to certain crystals of alum, white sulphuret of iron, &c., whose faces are wanting, and which consist of edges only. In spring and autumn; that is, between the season of snow and that of hail, the hail which falls partakes of the nature of both, is partly the one and the other; its crystals, though regular, are opaque, of little solidity, and consist, like snow, of an imperfect union of grains, or smaller crystals. A MEANS OF DISCRIMINATION BETWEEN THE SULPHATES OF BARIUM AND STRONTIUM. From Thomson's Annals of Philosophy, Vol. XXI; New Series, Vol. V, 1823, page 359. : April 2, 1823. SIR To distinguish barytes and strontian from one another, it is directed in No. 19 of the Journal of the Royal Institution to dissolve in an acid which forms a soluble salt with them, to decompose by sulphate of soda, and to add subcarbonate of potash to the filtered liquor. If the earth tried is strontian, a precipitate falls; if barytes, not. When these matters are in a state to be soluble in an acid, a more certain, I apprehend, and undoubtedly a much easier proceeding, is to put a particle into a drop of marine acid. on a plate of glass, and to let this solution crystallize spontaneously. The crystals of chloride of barium in rectangular eight-sided plates are immediately distinguishable from the fibrous crystals of chloride of strontium. I have not repeated the process above quoted; but if sulphate of strontium did possess the solubility in water there implied, this quality presented a ready method by which mineralogists would be enabled to distinguish it from sulphate of barium. On trial I did not find water, or solution of sulphate of soda, in which sulphate of strontian had long lain, produce the least cloud on the addition of what is called subcarbonate of soda. |