BARIUM, STRONTIUM, AND CALCIUM. 223 



the red flames making a brilliant display. B is a piece of 

 lead pipe fastened with copper wire to the case to hold it, 

 with its orifice downward. The oxygen in this mixture is 

 contained in the potassium chlorate and the strontium ni- 

 trate, while the sulphur and carbon are the combustible 

 substances. The red color is given to the flame by the 

 strontium nitrate. 



310. Calcium. This metal has no interest for us, but its 

 oxide and its hydrate, as well as many other of its com- 

 pounds, are of the greatest importance. Quicklime is cal- 

 cium oxide, CaO ; slaked lime is calcium hydrate, CaIT 2 O 2 . 

 We often use the word lime when we ought strictly to say 

 calcium. Lime is never found in nature, but abounds in 

 combination with acids. In this way it forms more than 

 half of chalk, limestone, and marble, is the base of plaster 

 of Paris and alabaster, and constitutes the greater part of 

 the mineral portion of the bones of animals. Lime is con- 

 sidered as occupying a middle place between the alkalies 

 and the earths. It is, therefore, called an alkaline earth. 

 The earths are insoluble, the alkalies are very soluble, but 

 the alkaline earths are but sparingly soluble. The alkaline 

 earths are also midway between the earths and the alkalies 

 as to being caustic, for they are somewhat caustic, while 

 the alkalies are very much so, and the earths not at all, but 

 perfectly inert. That lime is somewhat caustic you can 

 perceive by the feeling occasioned when you rub a little 

 of it, made into paste, between your fingers. It is from 

 this caustic quality that the milk of lime that is, lime dif- 

 fused in water is used to remove the hair from hides. So, 

 also, lime is often mixed with weeds to quicken their de- 

 composition. 



311. Manufacture of Lime. Quicklime is obtained from 

 the carbonate in its various forms chalk, limestone, marble, 

 oyster-shells, etc. simply by the application of strong heat, 



