354 SORGHUM. 



330, has been employed, with the sides and partitions higher, so that 

 a dejith of juice may be secured sufficient to cover a pipe through 

 which hot water circulates, by which the evaporation is kept up. In 

 like manner, hot water has been employed in the coils of the vacuum 

 pan, thus avoiding all danger of burning, which, by using steam, 

 may occur when the vacuum is not vvell kept, as through an insuf- 

 ficient supply of condensing water. Even in the vacuum pan, the 

 steam generated by the hot surface of the coils is yet under the pres- 

 sure of the superincumbent mass of syrup, which would be approxi- 

 mately 1^ pounds pressure, equal to 3 inches of mercury, for two feet 

 depth of syrup above the heated coil. It is obvious, therefore, that 

 the pan should be shallow in order to secure evaporation at the low- 

 est temperature ; but, in practice, it has been found to give better 

 results xn crystallization, by increasing the depth — a result which may 

 be due to the greater freedom of motion of the contents of the pan, 

 Avhich the higher temperature and the escape of steam from a greater 

 depth insures. We have seen that sugar is soluble in all proportions 

 in water ; or, rather, that the amount of water necessary to dissolve 

 sugar depends upon the temj^erature, see page 336. If, therefore, 

 the water which is present in a solution of sugar be evaporated by 

 boiling in an open vessel, it will be found that, as the water evapo- 

 rates, the temperature of the boiling liquid will gradually increase, 

 and the degree of concentration may be very accurately determined 

 by means of the thermometer. See page 336. 



No crystallization of sugar, therefore, can be secured in the open 

 pan so long as the boiling is continued; but it is found, after the con- 

 centration has been carried to a certain point, that the amount of 

 sugar is so much in excess of that which the water present is able at 

 ordinary temperatures to dissolve, that, if a portion of the boiling 

 syrup be taken from the pan, the crystallization of the sugar is al- 

 most instantaneous, and it is by means of a few simple tests that the 

 experienced sugar-boiler in charge of the Jamaica Train is enabled to 

 tell, when the contents of his battery or strike pan are ready to be 

 transferred to the crystallizing vessels. 



The method which is difficult to describe, but which is very simple 

 in practice, commonly employed, is to remove a portion of the boil- 

 ing syrup by the ladle, and observe its character and appearance, 

 as the last and partially cooled portion runs off; oi', by taking 

 a drop of the syrup between the thumb and fore-finger, gradually 

 opening them and observing the string of syrup formed, which, if of 

 the right character, may be extended to about an inch and a half be- 

 fore parting; the broken end partly curls up, while the string presents 



