ON MANGANESE 87 



gypsum or calx of tin. (I) But on keeping the glass for a 

 long time in fusion upon charcoal, by means of the blowpipe, 

 the colour does not disappear. Nay, if the colourless glass 

 (a) is kept in this state for a short time upon charcoal, by 

 means of the blowpipe, it grows red again, (c) If to such 

 a red glass globule a little sulphur be added, the colour 

 disappears. The same thing happens on adding a little of 

 any metallic calx, and any neutral salt containing vitriolic 

 acid. Here it is to be observed that all metals of which 

 the calxes colour glass, as for instance copper, iron, cobalt, 

 give their peculiar colour to the glass, while they deprive it 

 of the red colour communicated by manganese, (d) If to 

 such a colourless glass nitre be added, though even in the 

 smallest quantity, it immediately grows red again. The 

 same thing happens if such a colourless glass globule is 

 kept in fusion upon an iron plate for a few minutes, (e) 

 The appearance and disappearance of the red colour may be 

 produced at pleasure : by only keeping the colourless glass 

 apart from all phlogistic matter and in fusion for a few 

 minutes, it will grow red ; and then, by setting it upon 

 charcoal, it will effervesce and grow colourless again. These 

 last phenomena, however, will not succeed if the glass (a) 

 be made use of. 



From these experiments the following questions may 

 be answered : Whence does it happen that the additions 

 mentioned at letter (e) so suddenly destroy the natural red 

 colour of the manganese, since, sulphur excepted, they do 

 not contain any considerable portion of phlogiston that can 

 be separated from them, which, however, is necessary for the 

 destruction of the colour ? And why does not the red 

 glass upon the charcoal become colourless by itself under 

 the blowpipe, as happens on the addition of charcoal in 

 the crucible ? 



