A HISTORY OF SCIENCE 



and even the very critical were hardly likely to find 

 fault with the exchange thus made. Furthermore, it 

 was believed that gold possessed the property of chang- 

 ing its bulk under certain conditions, some of the more 

 conservative alchemists maintaining that gold was 

 only increased in bulk, not necessarily created, by cer- 

 tain forms of the magic stone. Thus a very proficient 

 operator was thought to be able to increase a grain of 

 gold into a pound of pure metal, while one less expert 

 could only double, or possibly treble, its original weight. 

 The actual number of useful discoveries resulting 

 from the efforts of the alchemists is considerable, 

 some of them of incalculable value. Roger Bacon, 

 who lived in the thirteenth century, while devoting 

 much of his time to alchemy, made such valuable dis- 

 coveries as the theory, at least, of the telescope, and 

 probably gunpowder. Of this latter we cannot be 

 sure that the discovery was his own and that he had 

 not learned of it through the source of old manuscripts. 

 But it is not impossible nor improbable that he may 

 have hit upon the mixture that makes the explosives 

 while searching for the philosopher's stone in his lab- 

 oratory. "Von Helmont, in the same pursuit, dis- 

 co verd the properties of gas," says Mackay; "Geber 

 made discoveries in chemistry, which were equally im- 

 portant; and Paracelsus, amid his perpetual visions of 

 the transmutation of metals, found that mercury was 

 a remedy for one of the most odious and excruciat- 

 ing of all the diseases that afflict humanity." 3 As we 

 shall see a little farther on, alchemy finally evolved 

 into modern chemistry, but not until it had passed 

 through several important transitional stages. 



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