BOHE-BLACE: w 



The bones lose upon an average about one-half of their weight in the calcination. 

 In reference to the quality of the black, experience has shown that it is so much more 

 powerful as a decolouring agent, as the bones from which it was made have been 

 freer from adhering fatty, fleshy, and tendinous matters. 



The charcoal is ground in mills with grooved rollers, in order to prevent the forma- 

 tion of dust. The bones are thrown into a long quadrangular box, furnished at its 

 lower aperture with moveable steel cheeks, between which the roller revolves ; they 

 are thus coarsely broken up, and the granulation is completed by another pair of 

 bluntly grooved rollers, which can be placed nearer to, or further from, each other at 

 pleasure. The crushed charcoal is collected on sieves, which separate the dust from 

 the grains. 



The composition of perfectly dry bone-black of average quality is as follows : 

 Phosphate of lime, with carbonate of lime, and a little sulplmret of iron, or oxide of 

 iron, 88 parts ; iron in the state of silicated carburet, 2 parts ; charcoal containing 

 about ^gth of nitrogen, 10 parts. None of the substances present, except the charcoal, 

 possess separately any decolourising power. 



It was formerly supposed that the peculiar absorbing and decolouring power of 

 animal charcoal was only exerted towards bodies of organic origin ; but it was found, 

 by Graham, that inorganic substances are equally subject to this action ; and later 

 experiments have demonstrated that there are few, if any, chemical compounds which 

 altogether resist the absorbing power of charcoal. The action is of a mechanical 

 nature, and in some cases it is sufficiently powerful to overcome chemical affinities 

 of considerable power. It is not confined to charcoal, though pre-eminent in this 

 substance, in consequence of the immense extent of surface which its porous structure 

 presents. The action of charcoal in sugar-refining has been particularly studied by 

 Liidersdorf. "When the defecated saccharine juice is allowed to flow upon a moist 

 and firmly compressed charcoal filter, pure water is the first product that passes 

 through ; but a considerably larger quantity is obtained than was employed for mois- 

 tening the charcoal. Water is then obtained of a decidedly saline character, which 

 increases in strength, and after this has passed through for some time, a sweet 

 taste becomes perceptible, which gradually increases, and at last entirely masks the 

 saline. This purely sweet fluid continues to flow for some time ; after which, the 

 liquid acquires an alkaline reaction from the presence of caustic lime ; it then becomes 

 coloured, the liquor getting gradually darker, till the action of the charcoal ceases. 

 Lime is completely abstracted from lime-water by bone-charcoal ; and, according to 

 the experiments of Chevallier, lead-salts are likewise entirely absorbed, the acetate 

 the most readily. It has also been shown by Graham, that iodine even is separated 

 from iodide of potassium. The commercial value of animal charcoal has usually been 

 estimated by its decolouring power on sulphate of indigo ; its absorbent power, which is 

 a property of equal, perhaps of greater importance, may, according to M. Corenwinder, 

 be determined, approximately, by the quantity of lime which a given weight will 

 absorb. For this purpose he employs a solution of saccharate of lime of known 

 strength. An acid liquor is first prepared, composed of 20 grammes of pure oil of 

 vitriol diluted with water to exactly 1 litre. A solution 'of saccharate of lime is then 

 prepared, by dissolving 125 to 130 grammes of white sugar in water, adding thereto 

 15 to 20 grammes of qiiicklime, boiling the liquid, and then filtering to separate the 

 undissolved lime. This solution is prepared of such a nature, that it will be exactly 

 saturated by the same volume of the dilute sulphuric acid. By adding the latter to 

 60 cubic centimetres of the liquid filtered from the animal charcoal, it is easy to see 

 how many degrees of the burette are required to complete the saturation of the lime. 

 Suppose 35 are required for this purpose, 10035 = 65, which represent the propor- 

 tion of lime absorbed by the charcoal : this is, therefore, the number representing the 

 standard, By operating with a burette graduated from the bottom, the degree of the 

 charcoal experimented upon may be read directly. 



This decolourising power does not belong alone to bone-black ; different varieties of 

 lignite, or even coal, when well carbonised in close vessels, afford a decolouring char- 

 coal of considerable value. By reducing 100 parts of clay into a thin paste with 

 water, kneading into it 20 parts of tar, and 500 of finely-ground pit-coal, drying the 

 mixed mass, and calcining it out of contact of air, a charcoally matter may be obtained 

 not much inferior to bone-black in whitening syrups. 



The restoration of animal charcoal from burnt bones, for the purpose of sugar- 

 refining, has been long practised in France. Mr. "W. Parker has made the following 

 process the subject of a patent. The charcoal, when taken from the vessels in which 

 it has been employed for the purposes of clarifying the sugar, is to be thoroughly 

 washed with the purest water that can be obtained, in order to remove all the saccha- 

 rine matter adhering to it. When the washing process has been completed, the char- 

 coal is laid out to dry, either in the open air or in a suitable stove ; and when pet- 



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