Progress of Foreign Science. 



413 



vhen they are tried with the indigo. Thus in the case of indigo 

 we find that the blanching power of blood-charcoal is to that 

 of bone-black as fifty to one ; and for the melasses, this propor- 

 tion is twenty to one. To find out what might be the cause of 

 this variation, he made the same trials on decoctions of cochineal, 

 logwood, gum, Sfc, and he observed that it always required 

 more charcoal to blanch the same bulk of liquor, the more the 

 relation between the discolouring power of the charcoals dimi- 

 nished ; that is to say, if we suppose, that we take the like vo- 

 lume of all the test-liquors, that which will require least char- 

 coal for its discoloration, is that which will establish the great- 

 est difference between the discolouring force of the different char- 

 coals. 



Table of the comparative discolouring power of different 



Charcoals. 



Vol.. XIII. 



2 F 



