326 History of Luminescence 



Beccari then described his experiments in detail, dividing the 

 materials tested into natural and artificial phosphori and each of 

 them into " fossils, vegetables and animals." He observed that the 

 time of excitation need not be long and that sunlight was better 

 than the sky and that the excitation was less if the sunlight had 

 passed through a glass window. He likewise noted that the duration 

 of phosphorescent light was frequently very short. 



Among inorganic materials tested and found to luminesce were 

 certain gems, earths of various kinds, marble, gypsum, limestone 

 and Iceland spar. Among products of plants and animals, wood, 

 seeds, sugar, bones, teeth, egg shells, shells of molluscs and many 

 other materials were observed to be natural phosphors, but no metal- 

 lic substance could be made to luminesce. 



Beccari considered that any manufacturing treatment of a natural 

 product made it an artificial phosphor and classed such materials as 

 linen and paper in this category. He became particularly interested 

 in the effect of heat and noted that before illumination, heating or 

 roasting (toasting but not actual browning) of material increased 

 its ability to phosphoresce, but that heating an already phospho- 

 rescing material decreased the light. He found, for example, that 

 paper is " a considerable phosphorus " but on heating becomes " so 

 splendid as to be in a manner a new phosphorus." The action of 

 gentle heat, not sufficient to fuse bodies, produced phosphors of the 

 white meat of poultry, nerves, glue, bread, nuts, oats, cheese, and 

 resins but not feathers, hoofs, or the white of eggs. However, the 

 dried yolks of eggs were good phosphors and Beccari recalled that 

 Lemery tried to make Homberg's phosphorus from eggs and suc- 

 ceeded with the yolk but not with the white. Beccari concluded 

 " in truth, the phosphorus in bodies roasted or newly burnt, seems 

 to be fixed in its oily, or as the chymists call it, its sulphureous 

 principle." 



Another kind of artificial phosphor was prepared by strong heat- 

 ing of various materials, as in calcination. The ashes of plants were 

 found to be good phosphors especially when mixed with sulphur 

 and the " tutty " from furnaces of blacksmiths. These artificial phos- 

 phors usually emitted a yellowish or reddish long lasting light, 

 while the light of natural phosphorus was short and white. Beccari 

 thought there might be " two species of phosphoric quality . . . one 

 of them the phosphorism of earthy bodies or limestone; and the 

 other the oleaginous or sulphureous phosphorism: following in this 

 respect the example of electricity, one species of which is for a like 

 reason called vitreous and the other resinous." 



In a second paper (1746) Beccari reinvestigated materials in which 



