CRYSTALLIZATION 65 



to crystallize at its leisure into solid blocks, which 

 Fryer very appropriately called concrete. This ought 

 to be a very cheaply produced article of commerce, 

 and the idea appeared to be sound. But unfortunately 

 the concrete never " caught on " in the market. In 

 these days of Brewers' sugar there might be a better 

 demand. 



Another method of rapid evaporation of juice in 

 the form of a thin mm was introduced about the same 

 time, called the Wetzel pan, the principle of which 

 was to heat the juice in a long trough in which slowly 

 revolved a long cylindrical wheel armed with a series 

 of discs, which constantly exposed, in its slow revolution, 

 a thin film of juice to the air, and thus set up a rapid 

 evaporation. Another form was to heat with steam 

 the wheel instead of the vessel containing the juice, 

 or to make the wheel to consist of a series of steam 

 pipes, placed either lengthways or round the circum- 

 ference. This method involved the expense of an engine 

 to drive it. At that time some of his brother sugar 

 refiners were one day explaining to Fryer the new 

 method of the Scottish refiners in boiling their yellow 

 sugars at a very low temperature, which not only 

 improved the colour but also enabled them to sell more 

 water in combination with the sugar. " Ah ! " said 

 Fryer, " that must be the wet sell process." 



The Aspinall pan was another early system of evapora- 

 tion by steam heat. The steam passed into a chamber 

 in the pan, through which the juice circulated through 

 a series of vertical brass tubes until it was ready to 

 crystallize, when it was drawn off. Many modifications 

 of "this" were introduced, but all had the serious defect 

 of over-heating the juice. Also, when the juice thickens 

 evaporation goes on with great difficulty because 

 actual ebullition, at the temperature necessary for that 



