EXTRACTION 233 



is placed upon a series of perforated shelves arranged inside a 

 steam-tight cylinder or tower. Water is admitted from the 

 top and trickles down over the material whilst steam is 

 admitted from the bottom. Superheated steam is sometimes 

 used. The material may thus be digested with a minimum 

 amount of water, and the sol passes out of the apparatus 

 and from the action of heat soon after it is formed. From 

 bones the sol obtained is of good colour, but is somewhat dull. 

 Several variants of this process have been patented. 



Another continuous system of extraction is that involving 

 the use of the Archimedean screw. The material is fed into 

 one end of a cylinder carried along and discharged at the 

 other end by the screw. The cylinder is of metal gauze and 

 is steam jacketed. (L,ehmann's patent, 1912.) 



Continuous systems, involving a battery of digest ors 

 connected by pipes, have also been devised. Arrangements 

 are made of course for admitting water and steam as required. 



REFERENCES. 



" Glue and Glue Testing," by S. Rideal, D.Sc., 2nd ed., pp. 47-56 and 61. 

 " Gelatine, Glue and their Allied Products," by T. Lambert, pp. 21-24 

 40, 42-44, 49 and 51. 



" Encyclopedic chemique," Fremy, tome x., p. 83. 



PATENTS. 



Edison : U.S.A. patent, 1902, 703204. 

 Bertram : Km-.lish patent. 1892, 951. 

 Dorenburg : German patent, 1911, 239676. 

 Lehmann : French patent, 1912, 441548. 



