Analysis by Spectrum-observations. 99 



eye requires the presence of l0 1 00 of a milligramme of chlorate 

 of potassium in order to detect the presence of potassium. 



Caustic potash, and all compounds of potassium with vola- 

 tile acids, give the reaction without exception. Potash sili- 

 cates, and other non-volatile salts, on the other hand, only 

 produce the reaction when the metal is present in very large 

 quantities. It is only necessary, however, to melt the substance 

 with a bead of carbonate of sodium, in order to detect potassium 

 even when present in a very small quantity. The presence of 

 the sodium does not in the least interfere with the reaction, and 

 scarcely diminishes its delicacy. Orthoclase, sanidine, and 

 adularia may in this way be easily distinguished from albite, 

 oligoclase, Labradorite, and anorthite. In order to detect the 

 smallest traces of potassium salt, the silicate requires only to be 

 slightly ignited with a large excess of fluoride of ammonium on 

 a platinum capsule, after which the residue is brought into the 

 flame on a platinum wire. In this way it is found that almost 

 every silicate contains potash. Salts of lithium diminish or 

 influence the reaction as little as soda salts. Thus we need 

 only to hold the end of a burnt cigar in the flame before the 

 slit, in order at once to see the yellow line of sodium and the 

 two red lines of potassium and lithium, this latter metal being 

 scarcely ever absent in tobacco ash. 



Strontium. 



The spectra produced by the alkaline earths are by no means 

 so simple as those produced by the alkalies. That of strontium 

 is especially characterized by the absence of green bands. Eight 

 lines in the strontium-spectrum are remarkable, namely, six red, 

 one orange, and one blue line. The orange line, Sr«, which 

 appears close by the sodium line towards the red end of the spec- 

 trum, the two red lines, Sr /9 and Sr 7, and lastly, the blue line, 

 SrS, are the most important strontium bands, both as regards their 

 position and their intensity. For the purpose of examining the 

 intensity of the reaction, we quickly heated an aqueous solution 

 of chloride of strontium, of a known degree of concentration, 

 in a platinum dish over a large flame until the water was evapo- 

 rated and the basin became red-hot. The salt then began to 

 decrepitate, and was thrown in microscopic particles out of the 

 dish in the form of a white cloud carried up into the air. On 

 weighing the residual quantity of salt, it was found that in this 

 way 0*077 grm. of chloride of strontium had been mixed in the 

 form of a fine dust with the air of the room, weighing 77000 

 grms. As soon as the air in the room was perfectly mixed, by 

 rapidly moving an open umbrella, the characteristic lines of the 

 strontium- spectrum were beautifully seen. According to this 



