188 



pretty commonly diffused, but owing to their close resemb- 

 lance to the compounds of Potassium, they were not recog- 

 nized as separate substances, in fact had it not been for this 

 new method, we should not have been able to distinguish 

 them from the well known alkali potash. 



Ccesium and Rubidium, occur in the water of almost every 

 salt spring; and they have likewise been found in the ashes 

 of plants, especially in those of beet-root, so that they must 

 be contained in the soil, but in all these cases the quantity 

 in which they are found is very minute. The mineral Lepi- 

 dolite contains a certain quantity of Rubidium, which now 

 may be obtained by the pound, but Ccesium is still extreme- 

 ly rare. 



In a similar manner the existence of another new metal 

 has been pointed out by Mr. Crookes, which is characterized 

 by a spectrum containing one bright green band and has been 

 called Thallium (QaXXocr, Green Shoot). This has lately 

 been prepared in somewhat larger quantities by Mr Lamy, 

 from the residue of the Belgian sulphuric acid chambers. 

 He finds that in sp. gravity and outward properties it close- 

 ly resembles lead, but that it possesses very peculiar chemi- 

 cal characteristics. 



To render the foregoing phenomena and the hypothesis 

 involved intelligible to those who may not have studied the 

 subject, it will be necessary to enter a little into detail. 



The image produced by decomposing a white sunbeam, 

 consists of certain brilliantly colored rays, but those rays 

 are crossed by spaces giving no light, dark lines, which dark 

 lines are always found in the same places in the solar spect- 

 rum. 



The spectra obtained from some artificial sources of light 

 exhibit the colored rays shading one into the other ; while 

 those produced by some others consist of a series of lumi- 

 nous bands, separated by dark spaces and these luminous bands 

 are frequently found to coincide with the dark lines of the solar 

 spectrum. 



