ARTIFICIAL LIGHTING 



223 



of any desired width and of varying thickness (Scientific American 

 Supplement, No. 1689)., 



Plate glass is made by the pouring of melted glass upon hot iron 

 plates; heated rollers flatten it out (Fig. 207). 



252. Artificial Lighting. Until about 1860 the only 

 common means of lighting were the fireplace, candles, and 

 oils. Among the oils used were lard, olive, and whale 

 (sperm) oils. The oils burn with a smoky flame; but by 

 the use of a wick they are drawn up (cf. 32), a little at a 

 time, and converted into vapor. It is this vapor that 

 burns. The oils have a very high boiling point; hence 

 there is little danger that the body of the oil will be set 

 on fire (c/. 122). 



Candles. The materials used for candles are waxes, 

 fats, and paraffin. Waxes are high-melting fats, just 

 as oils are low-melting fats (cf. 224). The making of 



Fig. 208. 



Modern Way of Making Candles, In some of the candle-moulding machines more than 



500 candles can be made at once. Courtesy of Homan and Company, 



Cincinnati, Ohio. 



