12 PHOSPHORESCENCE 
no substance surpasses in this respect sulphuret 
of barium. 
It is nowa long time since the cobblerof Bologna, 
in Italy, astonished and amused his friends with a 
peculiar substance since known as Bologna phos- 
phorus, Bologna stone, or Solar phosphorus, which 
shines brightly in the dark after having been placed 
in the sunlight for some time. This substance is 
sulphuret of barium. The cobbler prepared it by 
heating red-hot with charcoal a piece of sulphate 
of baryta, or Barytine, (Fig. 1,) a stone which he 
Fig. 1, 
picked up in the secondary strata of the Monte 
Paterno, where he found it in lumps of considerable 
weight.* The German chemist, Marggraf, used to 
prepare solar phosphorus by powdering down the 
stone, and making it into thin cakes, with a mix- 
ture of flour and water, before submitting it to 
calcination. This ‘‘ Bologna phosphorus” was the 
first substance known to become phosphorescent 
after insolation, and, consequently, it has been 
* Barytine is found abundantly in Derbyshire, Cumberland, 
the Isle of Arran, ete. 
