ESSAY V. 



Without contact the manganese cannot combine with the 

 phlogiston of the charcoal, and the glass globule touches the 

 coal only in one point, and thus takes the phlogiston only 

 from, that point ; all the remaining points are in contact 

 with the surrounding atmosphere, which deprives it of much 

 more phlogiston (Sec. xv. (c)) than it is able to get from a 

 single point of the charcoal, and thus the natural colour 

 of the manganese must remain (5). The case is quite 

 different in a crucible (a) ; for here the atmosphere touches 

 only a part of the globule, and the whole mass receives a 

 sufficient quantity of phlogiston from the surrounding char- 

 coal powder to repair the loss, whence a colourless glass 

 flux is produced. The same is the case when any vitriolic 

 salt or metallic calx is added to a borax-glass globule in 

 fusion under the blowpipe, and coloured red by manganese 

 (c). For, since these substances attract the phlogiston with 

 sufficient force from the charcoal, though they are dissolved 

 in the glass, as is well known from the conversion of the 

 vitriolic acid into sulphur, and the reduction of the metallic 

 calxes, and since manganese is able to separate the phlogiston 

 from metals (Sees, xvi., XXXVIL), it follows that in such a 

 glass globule there is much more matter present which 

 attracts the phlogiston from the point of the charcoal, upon 

 which the globule rests, as is likewise sufficiently evident 

 from the effervescence that takes place. If manganese 

 comes into contact with any such substance when it is on 

 the point of being converted into sulphur, or reduced, it 

 is in the same circumstances as if it were in contact with 

 an equal quantity of charcoal powder. Hence, therefore, 

 the glass must become colourless ; and though the air 

 every moment takes away phlogiston from the surface of 

 the globule that is exposed to its action, the manganese 

 will have, notwithstanding, a sufficient number of points 



