18 



CHEMICAL COMPOSITION OF LIVIXG MATTER 



Fig. 1 — Apparatus 

 for heating mer- 

 curic oxide. 



of a charred match into the mouth of the tube the pres- 

 ence of the oxygen gas will become evident by the in- 

 creased brilliancy of the glow, due to 

 the rapid union of the charcoal with the 

 Hberated ox3'gen. The presence of the 

 merciuy ^iU be seen in the drops which 

 condense on the cooled sides of the tube. 

 Such an experiment not only illustrates 

 the maimer in which a compoimd may 

 be separated into its elements, but also 

 demonstrates an important property of 

 oxygen, namely, that in its pure state 

 its affinit}' for carbon is much greater 

 than when mixed with other gases in the air. 



If we heat a mixture of manganese dioxide^ and potas- 

 sium chlorate and collect the hberated gas over water as 

 shown in Figure 2, it is pos- 

 sible to compare the imion 

 of sulphur and phosphorus 

 with tills pure product, 

 with the result when these 

 elements combined with 

 the mixed oxygen of the 

 air. In every case the 

 union is much more vio- 

 lent than when ordinary 



air is present, and results in more heat being Hberated. 



Oxidation and combustion. — Such unions of elements 



with oxygen as have been described in the preceding 



pages, are spoken of as oxidations and the compounds 



' The manganese dioxide midergoes no change, but merely facili- 

 tates the decomposition of the potassium chlorate. 



riG. 2 - 



-Apparatus arranged for obtain- 

 ing oxygen. 



