NATURAL PHILOSOPHY. 137 







and even in the milk of animals fed on crops growing in the Rhine 

 plain, on a non-granite soil, and in the human blood. In the mother- 

 liquors of tartaric acid manufactories, the lithia is found to be so con- 

 centrated as to be worth commercial extraction ; and the same may 

 be said of certain mother-liquors of saline springs. 



The spectrum reaction of potassium is not nearly so delicate as that 

 of sodium ; its spectrum yielding only two characteristic lines, one in 

 the outermost red, and the other far in the violet ray of the solar spec- 

 trum points at which the eye ceases to be sensitive to the rays. The 

 presence, however, of one thousandth of a milligramme of the metal 

 could be readily detected. 



The rays shown by the chlorides of barium, strontium, and calcium 

 are more complicated than those afforded by potassium, sodium, and 

 lithium, and require a somewhat experienced eye for their identifica- 

 tion. 1 They are, however, quite distinct enough to be easily recog- 

 nized, even when salts of these metals are mixed together ; for the 

 great advantage of this method of analysis is, that foreign matters 

 have no influence on the results, the chemists being able to detect with 

 certainty the different elements in a mixture containing the tenth of 

 a milligramme of the metals mentioned above. Sodium, with its yel- 

 low ray, first appears ; after that the well-defined red ray of lithium ; 

 next is seen the paler rays indicating potassium ; and, after these 

 rays have disappeared, they are replaced by those of calcium and 

 strontium, which remain visible for some tune. The absence of one 

 or other of these sets of rays shows the absence of the corresponding 

 metals. 



We are, then, by this method, placed in possession of an analytical 

 process of the most extraordinary delicacy, and can by means of it 

 easily make a qualitative analysis of a compound containing several 

 elements. Thus Messrs. Bunsen and Kirchhoff have been enabled to 

 exhibit the reactions of potassium, sodium, lithium, Salcium, and 

 strontium, in several mineral waters ; to show the bands of sodium, 

 potassium, lithium, and calcium in the ash of a cigar moistened with 

 hydrochloric acid, and to point out differences in the composition of 

 various limestones. 



New Metals. But the greatest triumph of Bunsen's and Kirch- 

 hoff 's new method of analysis, was the discovery of two new metallic 

 elements, belonging to the group of alkali metals. While working on 

 the residue of a mineral water from Kreuznach, in Germany, a spec- 

 trum was obtained which gave lines as simple and characteristic as 

 those of lithium and sodium, but which were blue, and were not refera- 



iThe spectrum yielded by a flame containing the vapor of strontium is charac- 

 terized by the absence of green lines. It contains, however, eight remarkable 

 lines, namely, six red, one orange, and one blue. To examine the intensity of the 

 reaction, Kirchhoff and Euusen threw up into the air of the room, in the form of 

 fine dust, 0.077 grin, of chloride of strontium, and thoroughly mixed the air by 

 rapidly moving an umbrella ; the lines immediately came out and indicated the 

 presence of the six-hundred-thousandth part of a milligramme of strontium. 

 The barium spectrum is distinguished by two very distinct green lines, by whi-.-h 

 the authors were enabled to detect with certainty one thousandth of a milli- 

 gramme of metal. Calcium gives a very broad and characteristic green line, and, 

 moreover, a bright orange line lying near the red end of the spectrum. Six ten- 

 milliouths of a milligramme of the chloride of this metal could be easily de- 

 tected. 



12* 



