410 Progfess of' Fuieign Scieme. 



We have seen that blood, calcined alone, yielded a charcoal, 

 which does not discolour, because its particles contract so 

 strong an aggregation, that they are not susceptible of combin- 

 ing with the colouring matters. But if instead of calcining the 

 blood alone, we calcine it mixed with an inert substance, with 

 phosphate of lime for example, which does ^nothing but oppose 

 the aggregation of the particles, we obtain a charcoal susceptible 

 of discolouring, and whose blanching power will be represented 

 by 12, assuming always for unity, the blanching power of bone- 

 black. If we calcine blood with very fine carbonate of lime, 

 its discolouring property becomes 18 ; finally, if we treat it 

 with potash, it may even rise to 50. It is needless to say, that 

 in these different trials, the charcoal was deprived of the pot- 

 ash, chalk, or phosphate of lime, with which it had been cal- 

 cined. 



We may easily understand all these results, by considering 

 that the first substance, phosphate of lime, acts simply by 

 operating the division, nearly mechanical, of the charcoal ; the 

 second acts already with a little more energy, for we observe that 

 the water of edulcoration contains a small quantity of ferro- 

 prussiate of lime ; finally, the potash not only attenuates the 

 particles of the charcoal, but by combining with all the foreign 

 principles which it contains, it must leave it in a certain state 

 of porosity, which M. Bussy regards as more favourable to 

 discoloration than division itself. 



In order to ascertain that charcoal truly enjoys the property 

 of discolouring, independently of the substances which are made 

 to act upon it, M. Bussy sought to procure pure charcoal, by 

 means of the decomposition of subcarbonate of soda with 

 phosphorus, and he succeeded in obtaining a sufficient quantity 

 to determine its discolouring power, which he found to be equal 

 to 12. 



He next tried lamp-black ; but in its natural state it con- 

 tains resinous matter, which prevents us from regarding it as 

 pure charcoal. To make it such, we must calcine it anew. In 

 this state it is capable of discolouring ; its blanching power 

 being expressed by 4 ; and although it is obviously less than 

 that of the preceding, it is enough to shew that the property 

 resides in charcoal, and that it may vary from 4 to 12, by the 

 mere effect of physical circumstances, very difficult to appre- 

 ciate ; for it could not be easy to establish a perceptible dif- 

 ference between these two charcoals. If instead of heating the 

 lamp-black by itself, we mingle it exactly with 15 or 20 times 

 its weight of pure carbonate of potash (that from calcined tar- 

 tar), and expose it >,o a very strong heat in a platina crucible, 

 it is observed that the mass becomes hard, compact, experienc- 

 ing incipient fusion in the parts contiguous to the crucible. If 

 we dissolve this mass in water, in order to separate all the pot- 



