408 Progress of J'hrcign Science. 



alkali, the residuum was treated with muriatic acid, which occa- 

 sioned an effervescence due to the decomposition of a little sul- 

 phuret of iron ; and the acid being boiled on the charcoal, car- 

 ried off the phosphate of lime, with a little lime and iron. This 

 charcoal so treated, discoloured still very well ; even better than 

 before. It was therefore improbable that this charcoal owed its 

 property to the presence of potash, unless indeed there had 

 been formed some alloy which could resist the action of muriatic 

 acid. To ascertain this point, he calcined the charcoal which 

 had been treated with the acid, but the ashes were not alkaline, 

 and contained no salt of potash ; they were a mixture of oxide 

 of iron and silica, forming a twelfth part of the weight of the 

 charcoal calcined. '' 



It is then in the residuum of the action of muriatic acid that 

 the discolouring property resides, and this residuum is composed 

 of charcoal, and iron in the state of a carburet probably, since it is 

 not acted on by muriatic acid, a little silica, which is only acci- 

 dental, and azote. To determine what might be the influence 

 of the azote, he took calcined blood alone ; 3 decigrammes of 

 this blood, burned with peroxide of copper, yielded 12 of azote 

 for 100 in weight of the charcoal. The proportion of azote is 

 very variable ; we may even fail to obtain any, if the charcoal 

 has been strongly enough heated ; but in all these cases this 

 charcoal is hard, brilliant, and docs not discolour. That result- 

 ing from the calcination of blood with potash, tried by the oxide 

 of copper, contains still a certain quantity of azote, also variable, 

 but much less than the first ; but as it is one of the characters 

 of azotized carbon to furnish hydro-cyanate of potash when we 

 calcine it with this alkali, he conceived that by treating this 

 charcoal with anew quantity of potash, he could remove from, 

 it still a portion of azote ; he treated it anew with potash, and 

 the quantity of azote which after the first calcination was 5 per 

 cent., was reduced after the second to 2 ; and at the third the 

 charcoal contained no longer a sensible quantity of it. Now 

 since this reiterated action of the potash merely augmented the 

 discolouring property of the charcoal to such a degree, that after 

 the last calcination it was equal to 50, that of bone-black being 

 1 , it follows that azote is without effect in discoloration ; and 

 consequently, it is not to this body that animal charcoal oives its 

 property. 



It remained to know if the discolouring property was not 

 owing to the combination of charcoal and iron, a combination 

 which resists, as we have seen, the action of boiling muriatic 

 acid; but whose presence cannot be denied, since we always 

 find iron in the residuum of the combustion of charcoal. This 

 quantity of residuary iron, however, is not constant, which shews 

 that the combination is not in any lixed proportion. It is ob- 

 served, that the quantity of iron is so much greater as tlie heat 

 WHS stronger, at whicli the potash and blood were calcined ; but 



