xxiv THE LIFE OF KARL WILHELM SCHEELE 



But what is worthy of notice is that this pigment was pro- 

 duced by Scheele at a time when there were no brilliant greens. 

 Schweinfurth or emerald green, it is true, had been pro- 

 duced as far back as 1712 by Eusz and Sattler at Schwein- 

 furt, a small Bavarian town, from which the pigment takes its 

 name, but though more brilliant it has even less body than 

 Scheele's green itself, its brilliancy all depending upon its 

 crystalline nature ; and although Scheele's green is duller, it 

 has the advantage of being amorphous and miscible with oil, 

 without losing but little of its original depth of shade, 

 whereas the moment it is attempted to grind Schweinfurth 

 green in oil the crystals to which it owes its colour are 

 crushed, all its pristine brilliancy disappears, never to be 

 recalled, and what remains is nothing but a mixture of 

 crushed pigmentary transparent crystals and oil of a sickly 

 pale pea-green colour, pitiful to look upon, compared with the 

 original brilliant emerald tint of the dry uncrushed pigment. 

 The exact method by which Schweinfurth green was first 

 produced rests in obscurity ; but at the present day the first 

 stage in the manufacture of emerald or Schweinfurth green 

 consists in the making of Scheele's green, in the very same 

 way as Scheele made it, and then converting the arsenite of 

 copper thus produced into Schweinfurth green or the aceto- 

 arsenite of copper by digestion with dilute acetic acid. The 

 Schweinfurth green is extensively used in the United States 

 of America to kill the Colorado beetle and such like insects, 

 otherwise both pigments are practically obsolete. 



Molybdenite and Plumbago, differentiation between. At this 

 time he also examined a new mineral, Molybdence mitens, which 

 was presumed to contain lead, but which Scheele showed was 

 quite free therefrom, and he prepared molybdic acid from it. 



1779. Plumbago. In this year he demonstrated that 

 plumbago consists nearly altogether of carbon. 



