VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. l6& 



apportioning the closes of medicines, and especially of vomits and purges, to 

 the ages and constitutions of different patients ? 



Concerning Cobalt, and the Preparations of Smalt and Arsenic. By Dr. David 

 Kriegy F. R. S. N° 2Q3, p. 1753. 



The cadmia, or cobalt, is a massy, heavy, grey shining stone, found in great 

 quantities in the mines about Shneeberg, and some other places of Herman- 

 duria. It is often mixed with marcasite, sometimes with silver and copper ore, 

 in the figure of hair. After the cobalt is picked out, and separated from the 

 common stone, it is beaten to powder by an engine or machine, commonly used 

 in mines, called a poolwork. By that operation the water carries away the light 

 stuff and sand, leaving the heaviest behind. 



This powder is afterwards put into a low and broad furnace, made on purpose 

 to separate the sulphur and arsenic, where the powder is spread all over, and 

 the fire, which is beneath and behind it, is forced to pass its flame along over 

 the powder, and so carry with it the arsenic in form of a smoke, which is after- 

 wards received by a low chimney, and out of that carried into a close channel 

 made of brickwork, of about 50 or more paces, where the arsenic by the way 

 sticks to the wall, in form of a yellowish white powder, which is taken out 

 every 6 months, and melted into whole pieces. The cobalt being thus roasted, 

 and smoking little more, is taken out when red-hot, cooled again, and gathered 

 for melting. Its colour, by that way of roasting, is turned a little more whitish. 



When they intend to melt it, the powder of the cobalt is mixed with pot- 

 ashes and powder of white flint-stones; the proportion of which is according 

 to the goodness of the cobalt, or as the smalt is to be made of a deeper or 

 paler colour; for instance, they take one part of pot-ashes, two parts of cobalt, 

 and three or four parts of flint. This mixture is put into large strong pot?, 

 standing in a hot furnace, six or eight pots in one furnace, where it stands 

 melting for five or six hours, changing into a blue glass, which is afterwards 

 taken out with a large iron ladle, and put into a vessel full of cold water, where 

 it cracks and becomes more tender, to be more easily powdered again ; but the 

 empty pot in the furnace is filled up again with the aforesaid mixture. And 

 thus they continue night and day, still maintaining the fire in the furnace. The 

 blue glass taken out of the water is powdered again by the common engine ; the 

 finest part being separated by a sieve, is put into a mill, and ground in water to 

 the finest powder, which by washing is further separated from the coarser parts. 

 The same is afterwards dried in small warm chambers, then put into barrels, 

 and thus sent away to several countries. 



If one of the melting pots happen to break, or to be very much burnt, so 



