THE MICROSCOPE IN CHEMISTRY. 115 



mal secretions in the form of little spheres or disks, con- 

 sisting of groups of radiating needles. In otoliths it is 

 often in minute hexagonal prisms with trilateral summits. 

 It is deposited from water in irregular forms, all of which 

 are grouped needles. Sometimes it assumes the rhombo- 

 hedral form, as in the oyster shell (Plate IV, Fig. 76). 

 In any doubtful case, test as described at pages 99 and 

 108. 



Lactate of I^ime gives microscopic crystals, consisting of 

 delicate radiating needles (Plate IV, Fig. 77). 



Oxalate of Lime occurs as square flattened octahedra, as 

 square prisms with quadrilateral pyramids, as fine needles, 

 and as ellipsoidal flattened forms, sometimes constricted 

 so as to resemble dumb-bells (Plate IV, Fig. 78). 



Phosphate of Lime is usually in the form of thin rhombic 

 plates (Plate IV, Fig. 79). 



Sulphate of Lime rapidly formed, as in chemical testing, 

 gives minute needles or prisms (Plate IV, Fig. 80). When 

 more slowly formed, these are larger and mixed with 

 rhombic plates. 



Soda Salts. Chloride of Sodium or common salt gener- 

 ally forms a cube, terminated by quadrangular pyramids 

 or depressions (Plate IV, Fig. 81). The crystals do not 

 polarize light. 



Plate IV, Fig. 82, represents crystals of oxalate of soda, 

 and Plate IV, Fig. 83, those of nitrate. 



Magnesia Salts. Ammonio-phosphate, or triple phosphate, 

 is often found in animal secretions. The most common 

 form is prismatic, but sometimes it is feathery or stellate 

 (Plate IV, Fig. 84). 



Sulphate of Magnesia forms an interesting polarizing 

 object. 



A most instructive series of salts may be made by 

 rapidly crystallizing some on glass slides, and allowing 

 others to deposit more slowly. In this way a set of speci- 

 mens may be prepared for comparison. 



