[Continued from page 166.] SPECIMEN OF CARMINE.—mdash;This beautiful pro duct is obtained from cochineal, and is so val uable an article as to be rarely met with i-a a state of purity. It is obtained by the follow ing process :—mdash;boil 12 pounds of filtered rain water in a tin vessel, and add to it four ounces of finely-powdered cochineal; boil it for five minutes, constantly stirring with a glass rod ; then add five scruples of alum in fine powder, perfectly free from iron; boil again for two minutes, remove the vessel from the fire, co ver it, and allow the contents to settle. As soon as the liquor is clear, pour it, while still hot, into glass or porcelain vessels, and suffer it to remain some days, covered from dust.—mdash; The alum gradually precipitates the coloring matter, in combination with animal matter and a little alumina. The precipitate is put on a filter, washed, and dried in the shade.—mdash; It is one of the most beautiful ,red colors used by painters. SEVERAL SPECIMENS OF WOOD PRESERVED BY CHEMICAL PROCESS.—mdash;All wood contains what is called albumen—mdash;an essential ingredi ent in vegetable bodies, entering largely into the composition of the sap. As long as this albumen is supplied with sufficient moisture, so long will it be liable to enter into a kind of fermentation, especially if placed in damp or ill-ventilated situations, and often even where the ventilation is perfect, and the atmosphere in its ordinary state of humidity. It a piece of green timber, containing this albumen in a perfect state of solution in the moisture of the wood, be employed in the construction of a house, the sAbumen undergoes fermentation and the rot and decay of the wood speedily follow. How is this waste and destruction of wood to be prevented ? To a certain extent, by thoroughly drying the timber in a current of air. This, however, takes considerable time to effect. For instance, a large piece ol oak requires exposure for eight or ten years to dry it completely. This is demonstrated by the fact that it loses weight for that period. We may apply heat to hasten the process of drying, but the wood, when exposed to the ordinary temperature of the atmosphere, ab sorbs moisture in quantity varying with the compactness of the wood. In a dry roorn without a fire, the quantity of water re-ab sorbed by wood, amounts, on an average, to ten per cent. As long as the albumen of the wood is supplied with sufficient moisture to render it soluble, so long will there be dan ger of dry rot. The best plan, therefore, to adopt, is to render this albumen perfectly in soluble, so that, however much moisture shall be absorbed, it cannot be brought into an ac tive state again. For this purpose Sir H. Davy recommended that the wood should be steeper! in corrosive sublimate—mdash;a salt called bichloride by chemists, which has the proper ty of forming an insoluble compound with the albumen, and thus preventing its further action. This process was commercially ap plied by Wm, Kyan ; but, from the great ex pense attending the preparation, and the fear that the use of this poisonous salt might prove deleterious to the health of persons coming in contact with it, the employment of corrosive sublimate has been abandoned.—mdash; Creosote oil, obtained from wood and coal tar, has been used with great success; but this also possesses a disadvantage, as it imparts a disagreeable odor, and increases the inflam mability of the wood. Same of the specimens exhibited by Mr. Payne are prepared, first, by injecting a salt of baryta into the pores of the wood, and then adding a solution of sulphate of iron. By this means a compact solid substance is lormed, which remains in the wood, thereby increas ing its weight, and partly converting it into stone. Sir W. Burnett — Co., have some spe cimens prepared by injecting chloride of zinc into the pores of the wood. This substance makes the albumen perfectly insoluble, even in sea water, does not communicate any color or odor to the wood, renders it less inflamma ble, whilst its use is perfectly innocuous in a sanitary point of view.
This article was originally published with the title "Riddle's Report of the Great Exhibition"