

1818.] Sir Torbern Bergman. 33? 



that it cannot be converted into them, and, therefore, that it is 

 entitled to be considered as a peculiar substance. He adopts 

 Scheele's notion, that silica is a compound of fluoric acid and 

 water; an opinion soon after refuted. 



10. On the Hydrophanous Stone. — This name was given by 

 Sir John Hill to certain stones which are opaque in the air, but 

 become transparent when plunged into water. They were sold 

 at an extravagant price. But the secret of these stones is here 

 revealed by Bergman. Various minerals, particularly opals and 

 chalcedony, exhibit this property. Such stones have hollow 

 cavities in them. When these cavities are filled with air, the 

 stone is opaque, in consequence of the very different refracting 

 power of the stone and the air. But when the cavities are filled 

 with water, the stone becomes transparent, because the refract- 

 ing power of water approaches more nearly that of the stone 

 itself. 



11. On the Earth of Gems. — This elaborate paper was first 

 published in 1777, and is not the least remarkable of Bergman's 

 labours. It contains the first attempt to give an accurate 

 analysis of the very hard stony bodies. The processes, though 

 rude, exhibit obviously the rudiments of our present processes. 

 Indeed Bergman must be considered as the original author of 

 the processes for analyzing mineral bodies by the moist way. It 

 would be useless to enter into details respecting his results, as 

 it is not surprising that they should be all inaccurate. Indeed 

 as he gives a very imperfect account of the bodies to which he 

 affixes particular names, it is not always easy to conjecture what 

 the mineral really was that he subjected to analysis. Pro- 

 fessor Jameson, for example, conjectures that the hyacinth of 

 Bergman was in reality a cinnamon stone. But I had an oppor- 

 tunity of seeing the veiy collections of hyacinths from which 

 Bergman's specimens for analysis were selected ; for they are 

 still in the University of Upsala, in possession of Professor 

 Afzelius ; and there cannot be the least doubt entertained that 

 they are true hyacinths. 



The next dissertation on the earth of the tourmaline stone 

 needs not be particularly noticed, as the analysis was conducted 

 precisely in the same way as the analyses of the gems. 



12. On the Fulminating Calx of Gold. — This paper, first pub- 

 lished in 1769, contains the first accurate account of the 

 properties of fulminating gold, the first attempt to ascertain its 

 composition experimentally, and to explain its fulminating power. 

 According to Bergman, fulminating gold is a compound of 

 oxide of gold and ammonia. Ammonia is a compound of azote 

 and phlogiston. When heat is applied, the phlogiston reduces 

 the gold ; and the azote being suddenly disengaged in its elastic 

 state, occasions the explosion. The theory of this remarkable 

 powder lias advanced but little since Bergman's time. Analogy 

 would lead to the suspicion that it is a compound of gold and 



