Phosphorescence 329 



phur was used for a material that burned or appeared to burn. 

 After the original disappointment in finding no gold or silver in 

 the Bolognian stone, the Italians designated an alkali and sulphur 

 as important constituents of phosphors. This conclusion was quite 

 correct. 



In 1749 the great German chemist, Andreas Siegmund Marggraf 

 (1709-1782) of Berlin, famous as the discoverer of sugar in beets 

 in 1747, endeavored to analyze the phosphor which he had prepared 

 from the heavy spar of Monte Paterno itself. He found that hydro- 

 gen sulphide was given off on addition of acids, leading him to the 

 conclusion that the material was a compound of a sulphur acid 

 and an alkaline earth, which he thought was calcium.^- Marggraf 

 made clear the purpose of calcination. Like Hoffmann (1700) he 

 was able to prepare phosphors from gypsum (CaSOi) , as well as 

 from the heavy spar of Germany, from limestone, marble, oyster 

 shells, calcite and chalk, but not from every sample. The materials 

 were dissolved in nitric acid, precipitated with sulphuric acid and 

 the precipitate calcined. Like Lemery, he emphasized that iron 

 mortars should not be used for pulverizing the stone but held the 

 material should touch the coals during calcination. Marggraf also 

 stressed the fact that the mineral to be calcined must come from a 

 special locality, in this respect differing from the Swede, Johann 

 Gottskalt Wallerius (1709-1785) , who believed all limestones could 

 be made into phosphors by calcination. In Wallerius' experiments 

 the acid used may have contained the impurities important for 

 success. 



John Canton and Benjamin Wilson 



One of the last of the eighteenth-century phosphors to bear the 

 maker's name was Canton's phosphorus, an impure CaS, prepared 

 in 1768 by John Canton (1718-1772) , a school teacher of London. 

 His method was simple, as follows: ^^ 



Calcine some common oyster shells, by keeping them in a good coal fire 

 for half an hour; let the purest part of the calx be pulverized, and sifted; 

 mix with three parts of this powder one part of the flowers of sulphur; 

 let this mixture be rammed into a crucible of about an inch and a half 

 in depth, till it be almost full; and let it be placed in the middle of the 

 fire, where it must be kept red hot for one hour at least, and then set 



^-The metal was actually barium, discovered as baryta in 1774 by C. W. Scheele. 



^3 J. Canton in Phil. Trans. 58:337-344, 1768. According to Hulme (1801), who 

 studied temperature effects, Canton's method was later modified by Bryan Higgins, 

 Operator to the Society for Philosophical Experiments and Communications, who 

 recommended calcining the whole oyster shells in layers with sulphur in the crucible. 

 (See A7in. der Pliysik 12: 224, 1802.) 



