MICROSCOPIC OBJECTS. * 91 



Fig. 181. Crystals of Carbonate of Lime, x 80. 



Chalk (see fig. 102), marble, limestone (figs. 191, 192, 194), 

 coral, &c. are composed of carbonate of lime. It also occurs 

 in bone, shells, &c., and is, moreover, often found in the animal 

 secretions. From it all the salts of lime may be formed. 



The drawing illustrates the various forms of the crystals as 

 seen under polarized light. 



These crystals may be mounted in balsam. 



Fig. 182. Crystals of Sulphate of Lime, x 100. 



The crystals of this salt of lime may be prepared by adding 

 sulphuric acid to chloride of calcium. Or it may be prepared 

 from carbonate of lime by the addition of the same acid. 

 The size of the tufts of needle-shaped crystals varies greatly. 

 The preparation from which the drawing was made was evapo- 

 rated from a hot saturated solution of the salt and mounted in 

 a cell with castor-oil. 



Sulphate of lime is found in its natural state as gypsum, 

 alabaster, selenite, &c. It often exists in hard water, which, 

 on the addition of carbonate of soda, is softened by preci- 

 pitating the lime as a carbonate. The salt is not very 

 soluble in water. 



N 2 



