MANUAL FOR SUGAR GROWERS. 133 



theoretical yield, or every 100 pounds of sugar in 

 the wash ought to yield from eight and three-quar- 

 ters to nine and a quarter gallons of proof-spirit. 



When the fermentation of the wash has ceased, the 

 alcohol is recovered by distillation, an operation 

 depending on the fact that alcohol boils at a lower 

 temperature than water, so that, when a mixture of 

 water and alcohol is boiled, the vapour which fii'st 

 escapes consists very largely of alcohol, the vapour 

 containing more and more water as the boiling con- 

 tinues, until at last it consists of little else than water. 

 The simplest form of still in which the operation of 

 distilling is conducted consists merely of a vessel in 

 which the wash is boiled, provided with a long tube, 

 usually coiled into a spiral form for convenience, 

 into which the vapour passes and in which it is 

 cooled as rapidly as possible ; this cooling is effected 

 by placing the coiled tube in water. 



The only improvement commonly employed in 

 this class of still consists in introducing one or two 

 vessels or retorts between the body of the still and 

 the condenser or worm. The use of these is to in- 

 tercept the heavier vapours, thus rendering the recti- 

 fication more perfect at one operation than it would 

 be if the whole of the vapour passed direct to the 

 condenser worm and so into the receiver. 



Alcohol having a density of .864, or 40 over-proof,* 



* The term proof-spirit is derived from the curious method of 

 testing in use many years ago. A little of the spirit to be tested 

 was poured upon a small heap of gunpowder, and the spirit 

 ignited. If, when all the spirit had burned away, the gunpow- 

 der also took fire, the spirit was said to be "above proof ; '' if, on 



