1 8 NON-METALLIC SIMPLE SUBSTANCES. PART I. 



exists in three different states the amorphous, which 

 has no form ; the graphic, which takes the form of small 

 hexagonal plates ; and that of octohedral silicon : hence 

 this substance is dimorphous. 



A singular analogy obtains between silicon and carbon : 

 the amorphous form of silicon corresponds to charcoal, 

 the graphic form of silicon corresponds to the graphic 

 form of carbon, and the octohedral form of silicon to 

 the diamond ; jet the chemical relations between the 

 two substances are very small. 



Silica has hitherto been considered to be insoluble 

 in pure water ; at least M. Bischoff states that only one 

 part of silica dissolves in 769,230 parts" of water; but by 

 a method hereafter to be explained, Professor Graham 

 has actually obtained a limpid solution of silica in pure 

 water. 



Boron is a constituent of boracic acid, a natural 

 production in Thibet and Monte Corbalo in Tuscany. 

 It is a greenish- brown solid, insoluble in water, but 

 when heated to' about 600 it burns in open air with a 

 vivid flame. 



Fluorine is a constituent of a very beautiful mineral, 

 well known as fluor spar, which is found in cubic crys- 

 tals of a green, yellow, or purple colour. Hydrofluoric 

 acid obtained chemically from the mineral is highly 

 volatile and extremely corrosive. 



Three of the non-metallic simple substances, chlorine, 

 bromine, and iodine, are connected by the most remark- 

 able analogies. They are marine productions, for chlo- 

 rine is obtained from common sea-salt and in greater 

 purity from rock-salt, both of which are compounds of 

 chlorine and the metal sodium. When sea-water is 

 evaporated, salt and a substance called bittern remain, 

 which contains a salt whence bromine is separated. 



Again, when kelp, the ashes of burnt seaweeds, is 

 purified from the carbonate of soda 'and the chloride of 



