412 Progrens of Foreign Scietice. 



Phosphate of lime ^ 

 Carbonate of lime / 



Sulphuret of lime > • • 88 



Sulphuret of iron y 



Oxide of iron . . j 



Iron in the state of a silicated carburet .... 2 



Charcoal, containing 6 or 7 per cent, of azote 10 



Too 



When we treat this charcoal with muriatic acid, it leaves a 

 residuum of about twelve per cent., which is a mixture of azo- 

 tized carbon, of silica and carburet of iron, so that the pure 

 charcoal appears to constitute not more than one tenth of the 

 primitive charcoal. It would consequently appear that since 

 the discolouring power resides in the carbon, that of this puri- 

 fied carbon ought to be ten times more considerable than that of 

 the crude charcoal ; but this is by no means the case, for the 

 discolouring power of the purified charcoal is only 1.5, that of 

 the crude being 1. To account for this apparent anomaly, we 

 must consider, as will be shewn in the next chapter, that v;hen 

 carbon blanches a solution, the colouring matter comes to be 

 deposited on its surface; of consequence, the more surface the 

 charcoal presents to the solution, the more easily will the disco- 

 loration occur. It is precisely the same effect, which is observed 

 in dyeing fine or coarse wool ; more colouring matter being re- 

 quired for the first, than for the last, in equal weights. Hence, 

 when we treat bone black with muriatic acid, its discolouring 

 force is found to be increased in the ratio of the foreign bodies 

 which we abstract, and diminished in the ratio of the extent 

 of surface which it loses ; so that it is the relation of these two 

 changes which determines the increase or diminution of its pro- 

 perties. None of the substances present in bone-black when used 

 by itself, except the charcoal, discolours. 



After establishing the difference which exists between the 

 blanching property of different charcoals relative to the solution 

 of indigo, it became interesting to know, if this relation would 

 be preserved for the different colouring matters. M. Bussy made a 

 testliquor with melasses ; itwas composed of one part ofmelasses, 

 diluted with twenty of water, in which he'tried the different char- 

 coals marked in the following table. The quantities acted on 

 were more considerable than those indicated in the table, but he 

 reduced them to one gramme for the sake of comparison. 



From this table we perceive ; 1st. that the same quantity of 

 the same charcoal discolours about ten times more of the indigo 

 liquor, than of that of melasses ; 2d. that the different charcoals 

 preserve, in reference to these two substances, the same order 

 in their blanching power, but that the proportion which exists 

 between them, when they are tried by the melasses, is less than 



