64 The Diamond 



occurring also in other precious stones, the phosphorescent light is most 

 brilliant and intensified in the diamond; and for this reason it would 

 seem plausible that the diamond should have held the foremost rank 

 among the stones luminous at night. 



There remains, however, a grave obstacle in the way of this explana- 

 tion, which must not be overlooked; and this is that the ancient authors 

 who have written on precious stones are entirely reticent on the subject 

 of their phosphorescent quality. It is indeed taught that this phe- 

 nomenon was observed for the first time only by the physicist Robert 

 Boyle in 1663. 1 This, of course, does not mean that it was entirely 

 unknown before that time, and that it could not have revealed itself to 

 a layman by a chance accident. 



M. Berthelot, 2 however, has discovered in the collection of Greek 

 alchemists a small treatise propounding the processes "of coloring the 

 artificial precious stones, emeralds, carbuncles, and hyacinths, after 

 the book drawn from the sanctuary of the temple." He believes that 

 artificial coloring of stones is said in this text to impart to them the 

 property of phosphorescence, and that there is no doubt that the ancients 

 made precious stones phosporescent in darkness through the employ- 

 ment of superficial tinctures derived from substances such as bile of 

 marine animals, the analogous properties of which are known to us. I 

 must confess that this conclusion, though emanating from so high 

 and respectable an authority, for whom I have a profound admiration, 

 is not quite convincing to me. First, it seems open to doubt whether 

 the Greek recipe really took the desired effect, as long as this is not 

 experimentally established; second, if it did, it does not furnish proof 

 that the ancients were acquainted with the phenomenon of the phos- 

 phorescence of precious stones, as we understand it, which is a physical 

 property inherent in the stone, while in the Greek text the phospho- 

 rescence is alleged to result from animal products brought in contact 

 with the stone, not from the stone itself. The text published by 

 Berthelot, while it may tend to prove that certain ancient alchemists 

 knew something about the phosphorescence of certain animal organs, is 

 not at all apt to show that the same tendency in precious stones was 

 familiar to them; on the contrary, it would be much more likely to have 



when gently heated, will emit a visible light. Its color varies with different varieties, 

 and is usually not the same as the natural color of the mineral. The tints exhibited 

 are usually greenish, bluish, or purplish. 



1 Bauer, Precious Stones, p. 138. 



2 Sur un proc6d6 antique pour rendre les pierres precieuses et les vitrifications 

 phosphorescentes {Annates de chimie et physique, 6th series, Vol. XIV, 1888, 

 pp. 429-432); reprinted in his Introduction a l'6tude de la chimie, pp. 271-274 

 (Paris, 1889). 



