NOTES. 



417 



off its edges A a, X a, a a, &c. Occasionally both these modifications take 

 place. 



Fig. 38. 



NOTE 161, p. 106. Prismatic crystals of sulphate of nickel are some- 

 what like fig. 62, only that they are thin, like a hair. 



NOTE 162, p. 106. Zinc, a metal either found as an ore or mixed 

 with other metals. It is used in making brass. 



C 



NOTE 163, p. 107. A cube is a solid 

 contained by six plane square surfaces, 

 as fig. 39. 



Fig. 40. 



NOTE 164, p. 107. A tetrahedron is a solid contained by four triangular 

 surfaces, as fig. 40 : of this solid there are many varieties. 



NOTE 165, p. 107. There are many varieties of the octahedron. In 

 that mentioned in the text, the base a a a a, fig. 38, is a square, but the 

 base may be a rhomb ; this solid may also be elongated in the direction 

 of its axis A X, or it may be depressed. 



NOTE 166, pp. 108, 186. A rhombohedron is a solid contained by six 

 plane surfaces, as in fig. 63, the opposite planes being equal and similar 

 rhombs parallel to one another; but all the planes are not necessarily 

 equal or similar, nor are its angles right angles. In carbonate of lime the 

 angle C A B is 105-55, and the angle B or C is 75-05. 



NOTE 167, p. 108. Sublimation. Bodies raised into vapor which W 

 again condensed into a solid state. 



NOTE 168, p. 109. The surface of a 

 column of water, or spirit of wine, in a 

 capillary tube, ie hollow ; and that of a 

 column of quicksilver is convex, or round- 

 ed, as in fig. 41. 



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