136 ANNUAL OF SCIENTIFIC DISCOVERY. 



bo illuminated by means of a lens, which throws a portion of the rays 

 from a lamp through a small opening in the side of the tube of the 

 telescope C. 



The metals experimented on by Messrs. Bunsen and Kirchhoff are 

 used in the form of chlorides purified with the greatest care. When 

 these are introduced into a jet of flame they volatilize to a greater or 

 less extent, and then communicate to the flame the special character 

 above alluded to. 



Of the wonderful delicacy of this new method of analysis, our read- 

 ers may obtain a realizing sense from the following description of an 

 experiment which a recent writer describes as witnessing in Prof. 

 Bunsen's laboratory. In a far corner of the experiment room, the 

 capacity of which was about 60 cubic metres (1 cubic metre = 35.3 

 cubic feet), was burnt a mixture of 3 milligrammes (0.0462 gr.) of 

 chloride of sodium (common salt), whilst the spectrum of the flame 

 was observed through the slit of the telescope. Within a few mo- 

 ments, when the vapor has time to diffuse itself throughout the lamp 

 flame, a bright and distinct yellow line was seen to cross the spec- 

 trum, which remained visible for a few minutes and then disappeared. 

 This was the sodium line ; for whenever sodium is present in the at- 

 mosphere of the lamp flame, and however combined with other sub- 

 stances, that particular line never fails to appear. In this experiment, 

 it was calculated, from the weight of the sodium salt burnt, and from 

 the capacity of the room, that there was present, suspended in one 

 part by weight of air supplied to the flame, less than one 20,000,000th 

 of a part of chloride of sodium vapor. But as the reaction of the 

 sodium on the spectrum could be easily observed in one second, and 

 as in this time the quantity of air heated by the flame could be calcu- 

 lated from the rate of issue from the flame, and from the composition 

 of the flame, the surprising result was arrived at that the eye, in this 

 experiment, was able to recognize with the greatest ease the presence 

 of the three-millionth part of a milligramme of chloride of sodium. 

 It must not, therefore, be a matter of surprise to find sodium distrib- 

 uted almost everywhere, especially in the atmosphere, in which is 

 almost always a sufficient quantity to show the sodium ray. The same 

 may be also said in a great measure of the rare metal lithium, which 

 gives two sharply-defined lines the one a very weak yellow line, 

 and the other a bright red line, both toward the extreme end of the 

 solar spectrum. 



In regard to the sensibility of the lithium reaction in the spectrum 

 analysis, it is stated that in a room of a capacity of about sixty cubic 

 metres was exploded a mixture of sugar-of-milk and chlorate of 

 potassa, containing nine milligrammes of carbonate of lithia. The 

 lamp, being placed at some distance off, became quickly colored, so 

 that the red ray could be distinctly visible in the spectrum. The 

 authors estimated that this sensibility reached the nine-millionth part 

 of the amount taken. 



Messrs. Bunsen and Kirchhoff found in their experimenting, greatly 

 to their surprise, that lithium, instead of being a very rare substance, 

 was one of the most widely distributed of the elements. They found 

 it in the water of the Atlantic ; in the ashes of marine plants ; in pure 

 spring water ; in the ashes of tobacco, vine leaves, and of grapes ; 



