92 FROM AN EASY CHAIR 



in order that the pearl may grow in size, whilst only 

 those with good-sized pearls are opened at once, in 

 order that the pearl may be extracted and sent to 

 market. 



There were great findings of pearls in the fresh-water 

 pearl mussels of the Scotch rivers in former days. In 

 the last forty years of the eighteenth century these 

 pearls were exported from Scotland to France to the 

 value of ^100,000. 



In the eighteenth century not only did they get their 

 pearls from European rivers instead of from the East ; 

 but, instead of being excited about the artificial pro- 

 duction of diamonds, they were driven wild with 

 astonishment by the demonstration of the volatilisa- 

 tion of these stones the disappearance of diamonds 

 into invisible vapour when sufficiently heated. That 

 the hardest stone in nature could be thus dissipated 

 into thin air seemed incredible. On Aug. 10, 1771, 

 a chemist named Rouelle invited to his laboratory 

 to witness this wonder a company comprising the 

 Margrave of Baden and the Princess his wife, the 

 Dukes of Chaulne and of Nivernois, the Marchionesses 

 of Nesle and of Pons, the Countess of Polignac, and 

 some members of the Academy of Sciences, includ- 

 ing the great chemist Lavoisier. Four diamonds 

 the largest belonging to the Count Lauraguais were 

 submitted before the eyes of all to the heat of a 

 furnace, and in three hours had completely evaporated. 

 There was, no doubt, room here for a mystification and 

 for the abstraction of the diamonds with a view to 

 dishonest appropriation. But no such purpose existed. 

 The experiment was a genuine one, and Rouelle and his 

 brother were honest investigators. They established 

 the fact, now demonstrated as a lecture experiment, 

 that the diamond is volatilised at very high temperatures. 

 A more celebrated "evaporation" of diamonds that 

 which is known as " the affair of the Queen's necklace " 



