CHEMISTRY OF THE POTATO. 71 



tissues, fibre, &c., remaining behind on the sieves, whence 

 they are removed, and used either fresh, or pressed into a 

 form of cake, as a feeding substance, chiefly for pigs. The 

 starch is then allowed to subside, and the liquor decanted 

 off, fresh water is given to it, until all the impurities are 

 washed away, when it is dried and rendered a marketable 

 article. As the disease frequently makes its appearance 

 long before the crop has arrived at its maturity, it has often 

 happened that the crop has been lifted at an early period 

 of its growth, in order to secure as much of it as possible 

 from further injury from the disease. In this case the 

 yield of starch has exhibited a variation in accordance 

 with the data already given. Thus a sack of potatoes 

 (240 Ibs.) averages, under ordinary circumstances, in 



August, about 23 to 25 Ibs. of starch. 



September, 32 to 38 



October, 35 to 40 



November, ,, 38 to 45 



February, 45 to 38 



March, 38 to 28 



April, ,, 28 to 20 



On the Continent potatoes are largely used for brewing 

 and distilling purposes, 1 the fermentative process being 

 set up in the starch, by the addition of yeast, in the same 

 manner as when barley or any other grain is used. In 

 this process the entire potato is used very beneficially 

 the only obstacle to the operations being the formation of 

 a compound of a most offensive character, known to 

 chemists as "fusel- oil, "which has to be separated from the 

 spirits before they can be used for any purposes of con- 

 sumption or manufacture. 



The stems or "shaws" of the potato are invariably left 

 on the field, and ploughed in when preparing for the fol- 

 lowing crop. Their inorganic composition has already 



1 By a return lately published, we find that in Prussia, for the year 1858-59, 

 the number of distilleries in operation was no less than 1551; and that the 

 potatoes used amounted to 3,418,584 scheffels, equal to 5,170,607 bushels. 



