190 Dr. Anderson on our Knowledge of the Chemical Elements. 



tions, and can be obtained as a white or yellowish matter insoluble in 

 bisulphuret of carbon. Deville, Sclirotter, and Magnus have made a 

 large number of curious observations on these points. 



Selenium, whicli in its usual condition is an amorphous and glassy 

 substance, can also be converted by heat into a crystalline mass insoluble 

 in bisulphuret of cai'bon, and into another kind of crystals soluble in 

 that re-agent. 



But probably the most remarkable among these changes is that 

 offered by Boron, which has been long known amorphous, but which 

 Deville has recently obtained in a crystalline form, in which it can 

 scarcely be distinguished from the diamond, and in another state in 

 which it resembles graphite. The diamond boron is obtained by 

 heating amorphous boron or boracic acid in contact with aluminium 

 to a high temperature, and then dissolving the aluminium in potash, 

 when the boron is left in colourless or reddish crystals belonging 

 to the square prismatic system, having a specific gravity of 2'68. 

 It is quite infusible and almost as hard as the diamond, indeed, M. 

 Deville entertains the expectation that it may possibly be econom- 

 ically employed for jewelling watches, and some similar purposes. 

 Graphitic boron perfectly resembles graphite in colour and crystalline 

 form. 



Silicon is capable of existing in similar forms. The graphite form is 

 obtained by heating silico-fluoride of potassium with aluminium, and then 

 dissolving out the latter with hydrochloric acid, when the silicon is left 

 in six-sided plates. By a modification of this process, and by the use of 

 zinc it can be obtained, in regular octohedrons, sometimes of considerable 

 size. Silicon appears to have a very remarkable tendency to combine 

 with copper, and confers upon it a great degree of hardness, so great 

 indeed that the alloy is to copper what steel is to iron, and may even 

 be used for making cutting in.struments. 



A large number of the more oxidizable metals have recently been 

 sepai-ated and more minutely examined, and their properties found to 

 be very different from those previously attributed to them. Their ex- 

 amination has been greatly facilitated by the improvement in the 

 processes for making sodium, which can now be obtained in very large 

 quantities. It is scarcely necessary to refer to Aluminium, which is now 

 so famiUar. But Lithium, Barium, Strontium, Calcium, may be men- 

 tioned as metals previously almost unknown, and which have recently 

 been more minutely examined. Lithium is remarkable as being the 

 Ughtest solid known ; its specific gravity is 0"589, being less than that of 

 any known liquid, so that it floats on naphtha, and must be preserved 

 in a vessel free from air. Barium, Strontium, and Calcium have all a 



