INTRODUCTORY. 17 



10. No Chemical Action in the Changes Noticed above. 

 In the alterations of form above alluded to there is no chem- 

 ical change that is, no change in composition. When iron 

 is melted, it is still iron ; when mercury freezes, it is still 

 mercury ; and when water freezes or is vaporized, it is still 

 simply water. The change that occurs in such cases is mere- 

 ly in the arrangement of the particles, and not in their qual- 

 ities. The change when the liquid, water, is converted into 

 the vapor that we call steam is a 



great change. The particles are 

 very much separated from each oth- 

 er, as you may realize by observing 

 the alteration in bulk as represent- 

 ed iitFig. 1. Here the large cube 

 represents the quantity of steam 

 produced from a quantity of wa- 

 ter of the bulk of the small cube. Yet with this immense 

 change there is no alteration of the composition of the water. 

 Let the steam be condensed, and it will be simply water. 



11. Forma of Matter as Affected by Chemical Causes. 

 Though many of the changes in the form of matter are un- 

 attended by any chemical action, there are also many others 

 which are produced by chemical causes. One of the most 

 striking examples of this we have in water. This liquid is 

 composed wholly of two gases chemically united. As a 

 large volume of steam condensed forms but a little water, 

 so the bulk of the gases required to form a small amount of 

 water is very great. So, too, there must be great conden- 

 sation when the three gases of which nitric acid is composed 

 unite to form that liquid. On the other hand, in some chem- 

 ical combinations there are great expansions of matter. 

 When any solid, for example, enters into the composition 

 of a gas, it must be expanded into a very large volume. 

 Thus when the solid, carbon, unites with the gas, oxygen, 



