CHEMICAL DIVISIBILITY. 37 



lected and cooled, we shall not find the red oxide in our receiver, 

 but in its place a colorless gas, whilst at the same time globules 

 of metallic mercury are found to be deposited in the cooler 

 parts of the apparatus (Fig. 5). 



The action of heat has consequently in this case produced an 

 effect entirely different from the effects spoken of heretofore. 

 There is no doubt that the first action of the heat upon the 

 oxide of mercury is an increased velocity of the motion of its 

 molecules and simultaneously an increase of its volume, but 

 afterwards a decomposition of the oxide takes place, and two 

 substances different from the oxide are liberated. 



One of these substances is a silvery-white, heavy, liquid 

 metal, the mercury; the other substance is a colorless, odorless 

 gas, which supports combustion much more freely than atmos- 

 pheric air, and is known as oxygen. 



Elements. We have thus succeeded in proving that red oxide 

 of mercury may be converted or decomposed by the mere 

 action of heat into mercury and oxygen. It is but natural to 

 inquire whether it would be possible further to subdivide the 

 mercury or the oxygen again into two or more new substances 

 of different properties. To this question, which has been ex- 

 perimentally propounded to Nature over and over again, we 

 have but one answer, viz., oxygen and mercury are substances 

 incapable of decomposition by any means as yet at our disposal. 

 They resist the powerful influences of electricity and heat, even 

 when raised to the highest attainable degrees of intensity, and 

 they issue unchanged from every variety of reaction hitherto 

 devised with the view of resolving them into simpler forms of 

 matter. 



We are, therefore, justified in regarding oxygen and mercury 

 as non-decomposable or simple substances, in contradistinction 

 to compound or decomposable substances, such as the red oxide 

 of mercury. 



All substances which cannot by any known means be resolved 

 into simpler forms of matter, are called elements ; all substances 

 which may, by one process or another, be subdivided or decom- 

 posed in such a manner that new substances with new properties 

 are formed, are called compound substances or compounds. 



While the number of known compounds exceeds many 



