442 



SCIENTIFIC RECREATIONS. 



powdered flints, from which all the gross matter has been eliminated, 

 Flint is not difficult to break, if made hot and thrown into cold water. A 

 stamper is then -used to break the flints. They are first ground in a mill and 



purified like the clay, then they are 



mixed and beaten, while moist, 



into u putty," and turned, or forced, 



into moulds. The handles are fixed 



on afterwards. The ware is baked 



for two days and glazed. The 



various colours are obtained by mix- Fig - 467-- runt mm. 



ing different clays and oxides iron or manganese. Biscuit 



porcelain is made by pouring a creamy mixture of porcelain 



earth into plaster-of-Paris moulds, and when a thin case has 

 Fig. 4 e6.-Stam P ers. formed within, the liquid is poured out again. It is then 

 dried in the mould and shrinks. The mould is taken to pieces, and the 

 thin biscuit porcelain is left. 



FELSPARS are very like the zeolites, except that the former contain no 

 water. Felspar crystallizes in a number of different forms. We 

 annex illustrations of specimens. This spar is found in rocks, 

 granite, gneiss, etc. One variety is the moonstone^ of a peculiar 

 lustre. Felsite is amorphous felspar. Albite contains soda 

 instead of potash. Labradoritc is nearly a pure lime felspar,, and 

 is remarkable for its colours, like a pigeon's breast. Spodnmene 

 is like albite, and leucite, soda-lite, etc., belong to this family. 



Fig. 468. Felspar. 



LAPIS-LAZULI is a felspar distinguished by its blue tint. 

 It was used for ultramarine colouring at one time, which 

 colour can also be made chemically. Lapis-lazuli is 

 found in Siberia and China. It is a mixture of 

 mineral species. Haiiyne is something like it. Obsi- 

 dian is a sort of black glass, and occurs in various 

 colours in vitreous masses. It is derived from the 

 fusion . of rocks, and is employed in the manufacture 

 of boxes, etc. Pumice stone bears a resemblance in 

 composition to the foregoing, but is porous, and so 

 called spongy. It contains both potash and soda in 

 some quantities. Pearlstone and pitdistone also attach 

 themselves to this family group. 



Fig. 469. Felspar crystal. 



The GARNETS possess many curious forms of crystals, which are 

 coloured and used as gems. Tourmaline is a very particularly useful 

 crystal, and is used in the investigations concerning the polarization of 



