418 Introduction to the Study of Science 



quicklime into a quart can that is standing on the bottom of an in- 

 verted pan to protect the table. Pour over the quicklime four ounces 

 of water. Cover the can with a glass plate except a small opening 

 through which steam may escape. Observe the temperature, the 

 boiling, the expansion of lime lumps, and their crumbling into powder. 

 The water, except that escaping as steam, unites with the quicklime 

 to form a new compound. 



The compound is a fine, white, dry powder. In chemistry 

 it is named calcium hydroxid because it is calcium oxid plus 

 water. It is a chemical compound, the product of a chemical 

 change (page 131), in which the properties of the original sub- 

 stances do not appear because of their complete change in 

 structure. The product is dry. A substance is wet only when 

 it contains free water. Starch and sugar contain water, which, 

 however, is not free. Weigh the product. Does the weight 

 suggest that the product is equal to the sum of the weights of 

 the lime and water, except for that lost in steam? 



How lime compounds change in air. Lime is often made 

 into whitewash or milk of lime, a thin paste about the con- 

 sistency of cream. When applied to walls, whitewash begins 

 at once to change slowly its chemical nature by absorbing and 

 combining with the carbon dioxid from the air. The product of 

 this change, calcium carbonate, is already familiar. The same 

 change occurs in lime plaster and mortar, but more slowly be- 

 cause of the larger proportion of lime contained in such mix- 

 tures. What change occurs when expired air is passed through 

 lime water? In the hardening of whitewash, plaster, and 

 mortar, what actually takes place is an exchange of partners. 

 The carbon dioxid from the air, as absorbed by the lime, replaces 

 and sets free the water, which is in turn taken up by the air as 

 water vapor. 



Chemistry and industry. The study of the changes that 

 occur in the manufacture of lime and in lime in its various uses 

 may suggest the importance of the study of chemistry. The 

 knowledge and control of chemical facts and processes are in- 



