350 Dynamic Theory. 



gravity of 4. 8. The second, beta, is dark, reddish-brown in monoclinic 

 crystals of a specific gravity of 4. 5, and soluble in carbon di-sulphide. 

 There is also a third, amorphous, kind with specific gravity of about 4. 3. 

 At a temperature of 100 the beta variety changes into the alpha sort 

 giving out heat in doing so. 



Boron also exists in two states. In one it is a fine amorphous, green- 

 ish powder and easily takes fire. A hot summer sun will touch it off. 

 The other sort crystallizes like diamonds and is nearly as hard , is trans- 

 parent and sometimes colorless. It is difficult to burn this variety even 

 in oxygen gas. 



Antimony. This metal is dimorphous ; that is, it crystallizes in two 

 forms of crystals, rhombohedrons and octahedrons. It is bluish-white 

 with specific gravity of 6. 7. But it is also obtainable in an amorphous 

 condition by means of electricity, in which form its specific gravit} 7 " is 

 5. 8. If this form is gently heated or struck, it passes into the crystalline 

 form, giving out great heat in doing so. 



Chlorine is an elementary gas which exists in two states ; one active, 

 the other passive. The activity depends upon light. When it is pre- 

 pared in darkness it is of a sluggish nature. It may be mixed with 

 hydrogen, and if kept in darkness the two will remain indifferent to one 

 another. But if the mixture be exposed to sunlight they will at once 

 unite with a great explosion. 



Isomerism. This word means having equal or similar parts, and it is 

 used to designate those bodies which are composed of the same elements 

 in equal quantities, but which are nevertheless possessed of different 

 properties. It amounts to the same thing as allotropism, but the latter 

 word is generally applied to elementary bodies, while isomerism is ap- 

 plied to compound bodies. There are a great many isomeric compounds, 

 and as mentioned before, the differences between two of the same name is a 

 difference in the form of their molecules, or in the way in which they are 

 put together. The dextroses and levuloses mentioned in chapters 27 and 

 28 are isomeric compounds. Woody fibre and gum are isomeric with 

 starch, all three containing carbon, hydrogen and oxygen in the same 

 proportions. There are a great many crystalline bodies whose molecules 

 are put together in a spiral twist, so that light, in passing through them, 

 has to bore through like an augur. And as before mentioned, it is obliged 

 to turn to the left in some bodies and to the right in others. There are 

 two sorts of Tartaric acid; a solution of one turns the beam of light to 

 the left, the other to the right. An examination of the crystals of this 

 compound shows them to be alike in every respect, except that they are 

 rights and lefts, that is, if one be held up before a mirror, its image in 

 the glass will represent the other. The chemical difference between 

 these two is slight ; but it is remarkable that the two may be made to 



