Page:The American Cyclopædia (1879) Volume III.djvu/68

BONE BLACK beer and water, and moulded into the form of cups, called cupels, which are used in the pro- cess of cupellation. This is separating silver or gold from lead, by melting the alloy of the metala in the cupel, and subjecting it to the action of a current of air, which oxidizes the lead, converting it into litharge. This is ab- sorbed by the bone ash as fast as it is produced, till the precious unoxidizable metal is at last left pure and alone in the cupel. The opera- tion is conducted in the same manner on the large scale and in small assays. When care- fully prepared, and freed from foreign matters by levigation, bone ash is called burnt harts- horn, and is used for cleaning jewelry. BONE BLACK, a black carbonaceous powder, obtained by grinding the product of bones burned in a close vessel at a red heat. The name ivory black should properly be limited to the finer and more expensive article pre- pared from ivory. The volatile products of the distillation of bones are an empyreumatic oil, fetid gases, and ammoniacal vapors. The latter may be collected, as they sometimes are, in forming with them salts of ammonia. The fixed products, which constitute animal char- coal, or bone black, consist of Carbon 9-6 Sulphate of lime 0-2 Carbonate of lime 8'6 Phosphate of lime 78'3 Phosphate of magnesia 1*8 Chloride of sodium 0'5 Silii'ate and sand 0'8 Protoxide of iron 0-2 Alkalies, and sulphur 0-5 100-0 The powder resembles that of vegetable char- coal, but is more dense and less combustible, and its ashes are not so readily soluble in sul- phuric acid as those of charcoal. The process of preparing the material varies according as the ammoniacal vapors are saved, or allowed to go to waste. In the former case the bones, cleaned of their fatty matters, are carbonized in cast-iron cylinders, which connect by a three-inch pipe with the condensing apparatus. The cylinders are kept at a red heat for 36 hours, when the charred bones are taken out, and the cylinders are refilled. The bones are then ground in mills. The volatile products are in some instances discharged under the fire, by which they are consumed, and their dis- agreeable odor destroyed. In this way also they aiford some heat, and save fuel. By the other process, the bones are put in cast-iron pots, which contain each about 25 Ibs., and these are put together in pairs, mouth to mouth, and luted. They are then piled up in an oven or kiln, the entrances to which are tightly bricked up, except those for the admis- sion of the flame from the furnace connected with the kiln, and the opening into the chim- ney. The pots are well heated for 16 to 18 hours by the flame playing around them, and this is increased by the combustible vapors which issue from the bones. Other arrange- ments have been contrived for consuming the disagreeable gases. The valuable property possessed by bone black is its absorbing com- pletely the color of organic solutions, and leav- ing the liquid clear and limpid ; this is greatly facilitated by heating the mixture to the boiling point. Vegetable charcoal possesses the same property also, but to a much less degree. From the year 1800 wood coal continued to be used for decolorizing crude sirups, for which pur- pose it was about this time recommended by LiJwitz, a chemist of St. Petersburg; but in 1811 M. Figuier of Montpellier discovered the greater efficiency of animal charcoal for this purpose, and this being employed the next year by Derosne and Payen, it has since super- seded the use of vegetable coal. Although this property of charcoal has been ably inves- tigated by distinguished chemists, as Bussy, Payen, and Derosne, it does not yet clearly appear upon what it is dependent, nor whether it acts mechanically or chemically. M. Bussy has shown that bone black used for decoloring an indigo solution in concentrated sulphuric acid, and this diluted with water, does not give the slightest trace of sulphate of indigo by repeated washings, but does of free sulphuric acid. Treated, however, with an alkaline wash, the charcoal gives up the indigo, thus ap- pearing as if it acted mechanically. The effi- ciency of the charcoal is greatly dependent upon its being in a minute state of division. The earthy matters combined with the carbon of bones, no doubt, have great influence in effecting this condition. Vegetable coal attains it to some extent, and the decolorizing property also, by being finely comminuted previous to charring, and mixed with pulverized pumice, quartz, or calcined bones, or with some chemi- cally acting ingredient, as carbonate of potassa. The most powerful deodorizer is charcoal ob- tained in the manufacture of Prussian blue by calcining animal matter with potassa. It is the purest form of charcoal, freed by the po- tassa from its nitrogen, and reduced by chemi- cal segregation to the finest particles. Carbon obtained by decomposing carbonate of soda also possesses this property in a high degree, from the fine state of division in which its par- ticles are found, so that it would appear to be by no means peculiar to animal charcoal. Even other substances than carbon are ob- served to possess the same property, as has been shown by E. Filhol, such as sulphur, arsenic, iron reduced by hydrogen, &c. Bone black that has been once used for refining sirups may be revived, so as to answer the same purpose again. The process consists in thoroughly washing out the saccharine matters absorbed, and in some establishments in dis- solving the lime, which is also taken up by the bone black, by fermentation in water acidulat- ed with hydrochloric acid. The charcoal is then again calcined in crucibles, or, as in France, in reverberatory furnaces. High steam is said also to restore its property, but this