262 Domestic Science 



180. In our previous work we have considered the 

 unit particle involved in questions dealing with energy 

 to be the molecule. For the purpose of explaining the 

 phenomena of chemistry, a new unit is needed. Mole- 

 cules are supposed to consist of exceedingly small 

 particles, termed " atoms " (Gr., a, without ; tome, 

 cutting), those substances the molecules of which have 

 only one kind of atom being the elements, while those 

 possessing different sorts of atoms in each molecule 

 are what we have previously termed compounds. 

 Chemical energy resides chiefly in the atoms. The 

 formation of new combinations of these, resulting in 

 the production of compounds, and the breaking up of 

 combinations already existent, simpler compounds or 

 elements being thus brought into being, cause changes 

 in the quantity of chemical energy present before and 

 after the actions are brought about. In the former 

 kind of change, " combination " or " synthesis " is 

 said to occur, while an action of the latter kind is 

 termed a " decomposition " or " analysis ". 



181. The equations we have hitherto used to 

 represent in brief the course of a chemical reaction are 

 not, strictly speaking. " chemical " equations. In these 

 fatter, much more information is provided as to the 

 probable nature of the chemical action concerned than 

 is to be found in our previous equations. Thus the 

 burning of carbon in air or oxygen is indicated by the 

 equation 



C + 2 = C0 2 . 



Here C is a symbol signifying " one atom of the 

 element carbon " ; 2 is a formula for " one molecule 

 of oxygen composed of two atoms of that element " ; 

 C0 2 is the formula for " one molecule of the compound 



