PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 461 



tliG same as the other alkali metals. The salts of rubidia resem- 

 bles those of potash and soda. The tartrates and the platinum 

 salts vary in solubility, otherwise it would be difficult to distin- 

 guish between them. 

 o 



It now remains to discover some mineral containing sufficient 

 rubidium to enable us to study its use in the arts. One of the 

 richest minerals is the lepidolite of Hebron, in Maine; according 

 to Johnson and Allen of New-Haven, this ore contains 0.24 per 

 cent of the oxide of rubidium. 



It is not probable that metallic Rubidium will ever play an 

 important part in the arts, but its salts may possess different medi- 

 cinal properties to potash and soda, just as lithia is given as a sub- 

 ttitute for those alkalies. What properties this alkali Avould 

 impart to glass also remains a question for the future. We may 

 discover it in sufficient quantities for use in the manufacture of 

 soap. 



CESIUM. 



This metal was discovered at the same time and under the same 

 circumstances as rubidium, by Bunsen and Kirchhoff. Bunsen, 

 in his capacity of Counsellor of State, is called upon for advice 

 in sanitary matters, and everything relating to mineral springs i» 

 submitted to him for examination. He had the residues from the 

 evaporation of an enormous quantity of the Duerkheimer Spring 

 sent to him. He took 80,000 pounds of this water, and was able 

 to prepare from it a few grains of the oxide of caesium upon which 

 to found his investigation into its properties. It appears to be 

 less abundant than rubidium, and the two are commonly found 

 associated together. Bunsen was not able to determine the atomic 

 weight of cesium with entire accuracy upon the small quantity at 

 his command, and this valuable work was accomplished by John- 

 son and Allen of Yale College. They give the atomic weight as 

 133., hydrogen being taken as unity. It has the highest atomic 

 weight of any of the elements excepting gold, which is 197. 



The salts of caesium produce sky-blue lines on the spectrum, 

 and hence the name. 



Cassium and rubidum, in all their compounds, resemble potas- 

 sium so closely that they cannot be distinguished from it by re- 

 agents or before the blow-pipe. They can ©nly be recognized bj 

 means of the spectroscope, and render that instrument indispensa- 

 ble to the analytical chemist. 



