182 CHEMICAL DISCOVERY AND INVENTION 



During its immersion a process of dialysis goes on, each cell of 

 which the tissue consists acting as a membranous bag through 

 which the sugar and any salts present pass pretty rapidly, while 

 the non-crystalline albuminous and gummy matters remain 

 behind. A series of tanks is employed into which the water is 

 pumped in regular order so that the fresh water is added to the 

 already partly exhausted pulp, while the extract is passed on to 

 the tanks containing fresh beet, and so a fairly concentrated 

 solution of sugar is ultimately obtained. This solution is then 

 treated with lime and afterwards with carbon dioxide or sulphur 

 dioxide gas. 



The insoluble precipitate, which contains a considerable 

 amount of organic matter, is then passed through a filter press, 

 and the clear liquid evaporated in vacuum pans till it begins to 

 crystallise. This method of extraction, by taking advantage of 

 the process of diffusion, is indispensable and could not be re- 

 placed without great disadvantage by any process of extracting 

 the juice by pressure. 



The study of aqueous solutions has also been applied to the 

 elucidation of problems connected with the formation of mineral 

 deposits* The ocean is the recipient of all the very numerous 

 substances washed out of the land by the action of rain, and the 

 consequent delivery of these substances by streams and rivers 

 into the sea. From the sea the water evaporates and passes 

 invisibly into the atmosphere, but there can be no return of the 

 dissolved salts to the land except in the form of spray carried by 

 the wind. In countries like England with an extensive coast 

 the amount of salt thus returned is considerable, as fine spray is 

 carried by strong winds a long distance inland. 



Deposits of rock salt have been formed by slow evaporation 

 of the water of such enclosed basins as the Great Salt Lake in 

 Utah, the Dead Sea, etc., into which streams bring soluble 

 matter and from which there is no exit. The consequence of 

 these conditions is that in the course of ages such water becomes 

 highly saline and deposits are formed at the bottom and round 

 the shores of such lakes. Naturally the salts which are least 

 soluble in water are deposited first if they are present in appre- 

 ciable quantities. Thus a bed of gypsum (hydrated calcium 

 sulphate) is usually present below deposits of rock salt, but as 

 salts of potassium and magnesium, partly in the form of sulphate, 

 are associated with the sodium chloride the products may be 



