138 ELEMENTS OF SCIENCE 



whole mass of different substances which thus make up 

 the solid substance of the globe are termed " minerals." 



As was pointed out in the last chapter, most of 

 these bodies can be resolved into other substances, and 

 ultimately into " elements" so called because they have 

 not been found capable of further chemical analysis. 

 There are about seventy substances which are thus pro- 

 visionally regarded as ultimate, and which, by most varied 

 and different degrees of chemical synthesis, compose all 

 those matters whereof the world consists. But however 

 varied may be the degrees of synthesis produced, the ele- 

 ments, as before said,* are always combined in each kind 

 of substance, in one exactly definite manner, as estimated 

 by weight. Of the various elements, some, at what to us 

 are normal, moderate temperatures, are aeriform. Such 

 are the gases before spoken of as oxygen or hydrogen," 3 ? and 

 also the gases nitrogen and chlorine, with various others. 

 All the metals are elements and are normally solid, though 

 mercury, as we know, is liquid. Amongst the metals 

 are calcium, silicon, aluminium, potassium, sodium, mag- 

 nesium, and arsenic. Other solid elements are carbon 

 (or pure charcoal), sulphur, phosphorus, and iodine. 



Oxygen at all ordinary temperatures is a colourless 

 gas, but it has lately been changed, by reducing it to an 

 extremely low temperature, to the condition of a blue 

 liquid. As we have seen, it has a great tendency to unite 

 itself with many other substances. When it unites 

 violently, the substance it unites with " burns." A 

 general process of union, such as the rusting of iron, may 

 be therefore called a slow combustion. Anything which 

 burns in the air, burns with far greater intensity and 

 brilliancy when plunged in oxygen. Nevertheless, though 



* See ante, p. 133. f See ante, p. 129. 



