318 History of Luminescence 



ability of the phosphor,-^ and that too much impurity (too long 

 grinding) is also detrimental. The effect of a trace of copper and 

 just the right amount of copper in modern preparation of phos- 

 phors is well known, but the variation of results of the early experi- 

 mentors must have been very discouraging. 



Lemery can be regarded as in large part expressing Homberg's 

 views. He appears to have been a born expounder, for he had an 

 explanation for any peculiarity. Regarding the action of the iron 

 and brass mortars, Lemery wrote: ^* 



So it seems there is something in Iron prejudicial to this quality [of 

 phosphorescence] and that on the contrary Brass is agreeable to the 

 Nature of the Stone. As to the Marble, Porphyry and Crystal, without 

 doubt they want the agreeable quality of the Brass, but they do not make 

 such a prejudicial impression as Iron. This bad quality of the Iron, it 

 may be, proceeds from the Vitriolick acid of this metal which unites 

 with the exalted Sulphur of the Stone, thereby fixing it, so that it hinders 

 the light from kindling it to make it shine, as I shall shew afterwards. 



Regarding the composition of the stone and the effect of calcina- 

 tion, Lemery wrote: 



The Bolonian Stone is full of Sulphur, but this Sulphur before its 

 calcination, is so well united with the other principles, which compose 

 the Stone, that it appears not at all: and it is no more luminous than 

 any other stone. The fire in which it is put opens its pores, and exalts 

 the Sulphur, of which a great part is lost in the Air, but there still re- 

 mains a great deal, which is stopped by the powder which is about the 

 Stone. 



If too much calcined the sulphur evaporates away and if too little 

 calcined the pores are not sufficiently opened. 



It is therefore certain by all Experiments, that the calcined Stone, 

 which gives light, contains a very exalted Sulphur, whose insensible par- 

 ticles are in motion upon the surface. 



These things being granted, which to me appear indisputable, I say, 

 That the calcined Bolognian Stone becomes luminous, when exposed to 

 light, because the light which is a fire, lightens the Sulphur which is 

 upon the surface, and makes it appear burning, the same way as the fire 

 lights Charcoal. 



Lemery then proceeded to explain in terms of the above theory 

 all the peculiarities observed. He held that the fire of the Bolognian 



** Marheinecken (1744) and Neumann (1740) both advised using no iron in the 

 preparation. 



''* Quotations from the James Keill translation of the eighth French edition. A 

 course of chymistry, 711-725, London, 1698. 



