552 SPECIAL METHODS OF DISCOVERY. 





dried ; they also made gunpowder from one part of sul- 

 phur, two of charcoal, and six of saltpetre, and employed 

 it for filling rockets and crackers. 1 



The discovery of phosphorus by Brandt may be con- 

 sidered to have arisen in a similar way. Towards the end 

 of the eighth century, Achild Bechil, a Saracen, distilled 

 a mixture of dried extract of urine, clay, lime, and pow- 

 dered charcoal, and thereby obtained an artificial carbuncle 

 which shone in the dark ' like a full moon.' 2 In the year 

 1669, phosphorus was again discovered in human urine as 

 ' a dark, unctuous, daubing mass,' by Brandt, a merchant 

 of Hamburg, while searching for a liquid capable of 

 transmuting silver into gold. By applying heat to oxide 

 of mercury, Priestley in the year 1774 discovered oxygen, 

 and by heating black oxide of manganese to redness, 

 Scheele in the following year re-discovered that gas. 



The discovery of hyponitrous acid is also an instance of 

 the effect of heat upon substances. ' Mr. Grahn happening 

 to be one day in the shop of Mr. Loock, that gentleman 

 mentioned to him a circumstance which had lately oc- 

 curred to him, and of which he was anxious to obtain an 

 explanation. If a quantity of saltpetre be put into a 

 crucible and raised to such a temperature as shall not 

 merely melt it but occasion an agitation in it like boiling, 

 and if, after a certain time, the crucible be taken out of 

 the fire and allowed to cool, the saltpetre still continues 

 neutral, but its properties are altered; for, if distilled 

 vinegar be poured upon it, red fumes are given out, while 

 vinegar produces no effect upon the saltpetre before it has 

 been thus heated. Mr. Loock wished from Grahn an 

 explanation of the cause of this phenomenon ; Gahn was 

 unable to explain it, but promised to put the question to 



1 See Draper, Intellectual Development of Europe, p. 303. 

 Ibid. p. 304. 



