196 CHEMISTRY. 



Fig. 84. Lagoons of Tuscany 



these vapors are made to pass into water, which condenses 

 them, and then the water is evaporated, which leaves the 

 boracic acid in large crystalline flakes, having the feeling 

 somewhat of spermaceti. Boracic acid is not volatile when 

 it is by itself. If heat be applied to it, it will melt, and be- 

 come a vitreous mass, but no degree of heat will make it fly 

 off in vapor. But it is volatile when it is in volatile com- 

 pany, as we may say ; which is often true of other substan- 

 ces, and, we may add, persons also. Thus, if we mix some 

 of it with alcohol in a mortar, and then set fire to the alco- 

 hol, it will burn with a green flame, because some of the 

 boracic acid rises in vapor with it. Boracic acid forms 

 with sodium a bi-borate, commonly called borax, which 

 we shall notice hereafter. 



QUESTIONS. 



258. In what does silicon resemble carbon ? What are silicates ? 259. 

 What is said of the occurrence and abundance of silica ? What is quartz ? 

 What is granite ? What is clay ? 2GO. What is said of the presence of sil- 

 ica in plants ? What animals contain silica ? 261. What is silicified wood ? 

 Explain the error of common opinions regarding it. 2G2. How is glass 



