PHOSPHATES. 3l7 



the addition of a smaller boiler, in which the water is 

 first heated, arid its sediment deposited. 

 Give the sta- 803. STALACTITES. The masses of car- 

 lactites. bonate of lime which hang like mineral 



icicles from the roofs of caverns are called stalactites. 

 The water that penetrates the soil is the architect of 

 these curious forms. Impregnated with carbonic acid, 

 derived from decaying vegetation, it takes up its load 

 of carbonate of lime as it settles through the rock, and 

 deposits it again on exposure to the air of the cavern, 

 in various and often fantastic shapes. Another portion 

 of water, dripping to the floor of trje cavern, builds up 

 similar forms, called stalagmites, from below. 



804. ARTIFICIAL MARBLE. The surface 



How ts artifi- 



rial marble of wood or stone may be marbled by cov- 

 produccd? ering it with successive coats milk of lime, 

 and allowing each in turn to dry before the next is ap- 

 plied. The surface is then smoothed and polished, and 

 carbonic acid finally applied, by which it is converted 

 into marble. The milk of lime is simply a mixture 

 of slaked lime and water, and may be so colored as to 

 produce a variegated surface. 



PHOSPHATES 

 Describe the 805. PHOSPHATES. The phosphates, 



phosphates. w j th the exception of those of the alka- 

 lies, are, for the most part, white insoluble salts. 

 Phosphate of lime may be taken as an ex- 

 ample. The white residue which is obtained 

 on heating the bones of animals, until all the 

 animal matter is destroyed and expelled, is principally 

 phosphate of lime. 



