316 



SALTS. 



experiment is more striking, if the sal volatile is warmed 

 in a cup or other vessel. This salt is sometimes 

 used by bakers for making bread and cakes light and 

 spongy. 



800. CARBONATE OF LIME. Carbonate 

 of carbonate of lime, in the form of chalk, marble, arid 

 of ime? ordinary limestone, is a most abundant 

 mineral. Whole mountain chains consist of the latter 

 rock. The shells of shell-fish are principally carbon- 

 ate of lime. There is good reason, indeed, to believe 

 that all limestones have their origin in accumulations 

 of such shells, which have been consolidated in the 

 course of ages. 



801. SOLUBILITY IN CARBONIC ACID. 

 The solubility of carbonate of lime in 

 carbonic acid is readily shown, by passing 

 a current of the gas through 



water clouded with pulver- 

 ized chalk or marble. Other mineral 

 substances which form the food of plants 

 are dissolved by the same means, and 

 then find their way into the roots, to 5 

 subserve the purposes of vegetable life. 



802. INCRUSTATIONS IN BOILERS. Car- 



What is said 



of incrusta- bonate of lime dissolved in carbonated 

 twns m boil- water j s a g a i n precipitated on boiling the 

 solution. This is owing to the escape of 

 the acid. Incrustations in tea-kettles and steam-boilers, 

 in limestone districts, owe their origin to the same cause. 

 In some cases, the crust is formed of gypsum, or other 

 earthy matters contained in the water. One method 

 of avoiding this inconvenience in steam-boilers, is by 



How is the 

 solubility of 

 carbonate of 

 lime in car- 

 bonic acid 

 shown ? 



