Progress of Foreign Science. 415 



tered, and were found differently discoloured, according to the 

 species of charcoal which had acted upon it. Each of these 

 charcoals having been washed, and then dried at the water- 

 bath, taking every precaution to place them in the same cir- 

 cumstances, it happened that 



The blood-charcoal was increased in weight by 1.56 gr. 

 The purified bone-black .... 0.54 

 The crude bone-black .... 0.3 

 This increase of weight, which is, as we see, relative to the 

 blanching power of each charcoal, indicates that the discolor- 

 ation is effected by the combination of the colouring matter 

 with the charcoal. The same effect is also remarked, when we 

 employ indigo ; but it is much less appreciable. We have 

 reason, indeed, to l)e surprised at the considerable augmenta- 

 tion of weight which charcoal assumes in the discoloration of 

 melasses ; but it is probable, that this increase proceeds not 

 only from the colouring matter, if there exists a particular one, 

 but also from the mucilaginous matters, and others which are 

 not in perfect solution. It is a fact, well known to refiners, 

 that the waters of the charcoal washings which have served for 

 clarification, are very mucilaginous. If, instead of taking cold 

 water to wash this charcoal, boiling water be taken, slightly 

 alkalized with potash, the water comes off coloured of the 

 melasses tint, which further confirms the conclusion to be drawn 

 from the augmentation of the weight of the charcoal, namely, 

 that the colouring matter combines with the charcoal, without 

 experiencing decomposition. 



But this truth seems to be established in an incontestable 

 manner, by an experiment which M. Bussy made on indigo. 



Into a solution of indigo by sulphuric acid, made with one 

 part of indigo, and 7 parts of acid, the whole diluted with 92 

 of water, he added a certain quantity of charcoai which com- 

 pletely discoloured it. The liquor thrown upon a filter, passed 

 through with a slight tint of yellow, visible only in a great 

 mass of the liquid. The filter was washed with a small quan- 

 tity of cold water, to remove what of the solution remained 

 adhering to the filter ; this water passed colourless. He threw 

 afterwards on the same filter, boiling water, containing a very 

 small proportion of sub-carbonate of potash ; instantly the liquor 

 passed through of a blue colour, not of a feeble and uncertain 

 tint, but with an intensity of shade, equal to that of the first 

 solution. It is possible, by continuing the washing with very 

 hot alkalized water, to remove from the charcoal almost the 

 whole of the indigo which it contains. 



If we take again this same washed charcoal, and put it in 



contact with the bhic liquor of the washings, after rendering it 



slightly acid by the addition of a little sulphuric acid, it will 



discolour it anew, and the indigo fixed in the charcoal may be 



2 F 2 



