252 DISCOVERY CH. 



process. The chief method now used for the extraction 

 of gold from its ore is the cyanide process, and it enables 

 large quantities of the precious metal to be obtained 

 from residues which in the absence of this process would 

 be waste tailings. 



The first gas ever liquefied was chlorine, and when 

 Faraday succeeded in transforming it by pressure into 

 the liquid state he opened a new era of benefit to man. 

 Liquid air, liquid oxygen, and liquid hydrogen, are all 

 now commercial articles and not scientific curiosities. 

 Large quantities of sulphur dioxide and ammonia in the 

 liquefied form are now used for the artificial production 

 of ice, and for the refrigerating machinery which enables 

 fruit, meat and other articles of food to be transported 

 from their place of origin to distant parts of the earth in 

 a fresh condition. 



Sir James Dewar, working at the Royal Institution, 

 where Faraday made his pioneer experiments on the 

 liquefaction of gases, worthily carried on the work there, 

 and succeeded in reducing the most intractable gases to 

 the solid as well as the liquid form. A device adopted 

 by him for retaining liquid air and other liquefied gases 

 became later an article of commerce in the form of the 

 Thermos or vacuum flask. An instrument devised 

 originally for a scientific purpose has thus been converted 

 into an everyday commodity by which liquids can be 

 kept at a constant temperature for many hours. Before 

 it was generally realised that the vacuum flask had not 

 been patented, certain manufacturers made small for- 

 tunes out of it by charging a guinea for what had 

 cost about a shilling to produce ; but neither then nor 

 later has the actual inventor of this scientific device 

 reaped any pecuniary reward for his ingenuity. 



Saccharin, which has an intensely sweet taste, and is 



