S70 NINETEENTH CENTURY. pt. hi. 



draws it out, leaving the copper to fall down as a metal. 

 This was the method chiefly worked out by Bergmann in 

 1761, and which has since then been brought to much 

 greater perfection by other chemists. 



Secondly, by heating substances gently and examining 

 the vapours which rise from them, and afterwards analysing 

 what remains by burning. This method was fairly under- 

 stood by Geber, and was first applied to organic substances 

 by Boerhaave. 



Thirdly, by passing an electric current through a com- 

 pound substance in a fluid state, and so overcoming the 

 force which holds the difl"erent elements together and 

 setting them free. This method, called electrolysis^ was dis- 

 covered by Davy in 1806, and afterwards thoroughly worked 

 out by Faraday. 



Fourthly, there is the method of spectrum analysis 

 suggested by Herschel in 1822, which was carried on with 

 great success by Bunsen and Kirchhoflf. In this method 

 the substance is turned into gas either by ordinary heat or 

 by the electric spark, and is then examined by the spectro- 

 scope ; the elements being determined by the position of 

 the bright lines they throw on the spectrum. 



There is still a fifth method, about which we have 

 said nothing as yet, and which was chiefly brought into use 

 by the chemist Berzelius (mentioned p. Z^^i), namely the 

 fusing of substances by means of the blowpipe. This 

 instrument is merely a little tube with a mouthpiece at one 

 end and a very minute hole at the other. By placing the 

 minute hole in the middle of a flame and blowing through 

 the mouthpiece, the centre of the flame is made to burn 

 furiously, and many substances can be melted and decom- 

 posed by it which do not yield to ordinary heat. 



