6 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



largely in their natural condition as building materials, 

 but were also converted into lime by the action of heat and 

 used in the preparation of mortar. SAND was used with soda 

 in the manufacture of glass. 



Many crystals and precious stones were also known and 

 valued for personal adornment and for decorative purposes. 

 Amongst the first to attract attention were probably EMERALD, 

 TOPAZ, DIAMOND (Fig. 4), and QUARTZ (Fig. 5) ; the last 



FIG. 5 CRYSTALS OF QUARTZ. 

 British Museum (Natural History) 



gave 



substance, known also as ROCK-CRYSTAL, or CRYSTAL, 

 its name to the whole of this class of substances. 



Substances of organic origin, Many of the substances 

 known in ancient and mediaeval times were formed by the 

 agency of living organisms, either animals or plants. Among 

 these may be mentioned SUGAR (in the form of honey), 

 TURPENTINE, OILS, FATS, and WAXES (extracted from plants 

 and from the bodies of animals), AMBER (a fossil resin), and 

 PEARLS. WINE and VINEGAR were obtained by fermentation 



