APPENDIX. 95 



tumbler of water. They have disappeared. What has 

 become of them? They are held in solution in the 

 water. Now let the water be boiled down, or slowly 

 evaporated, and the salt and sugar will become again 

 visible in the form of crystals. 



Dissolve in water as much alum as it can take 

 up. When the water can dissolve no more it is said 

 to be saturated. Let the solution of alum remain un- 

 disturbed for a few days, in a warm place, and, as the 

 water is carried off by evaporation, the alum will be 

 restored to the crystalline form. Explain how the soil 

 becomes dry and parched, in the hot weather of sum- 

 mer, by this process of evaporation. 



23. The tables on the 43, 45 and 47 pages, should be 

 printed on a large sheet of pasteboard, and hung up in 

 the school-room. They will suggest many important 

 questions, and familiarize the class with the facts they 

 contain. 



24. Explain the terms by which chemists denote the 

 different kinds of saline substances, or of alkalies in 

 combination with acids. Thus, when nitric, sulphuric, 

 muriatic, carbonic or phosphoric acid, combine with the 

 alkali soda, they form the nitrate, sulphate, muriate, 

 carbonate or phosphate of soda. If they combine with 

 lime, then we have the nitrate, the sulphate, the muri- 

 ate, the carbonate or the phosphate of lime. 



When the nitrous or sulphurate acids combine with 

 alkalies, the salts formed are called sulphites ; thus we 

 have the sulphite of soda, or the nitrite of lime. 



