340 THE POTATO AND ITS COMMERCIAL PRODUCTS. 



grains are usually rather larger. The actual size of the grains varies from 

 irw to ^j of a line in diameter. The shape of the larger particles is ovate. 

 The quantity of starch obtained from potatoes, as we have already 

 shown, is subject to considerable variation. The proportion in 



100 parts of the kidney potato is 28 to 32, Dr Pearson. 



„ „ potato, various shaws 18 „ 8, Vauquelin. 



„ „ Champion 15 „ 9 



„ „ Chair rouge 12 „ 2 



„ „ L'Orpheline 24 „ 2 



All starch in potatoes is confined very near the surface ; the heart con- 

 tains but very little nutriment. Ignorance of this fact may form a 

 very plausible excuse for those who cut off thick parings in preparing 

 potatoes for cooking, but none to those who know better. Circulate the 

 injunction, " Pare thin the potato skin." 



In manufactories, the maximum quantity of starch obtained rarely 

 exceeds 18 per cent ; and it deserves especial notice that frosted potatoes 

 yield as much fecula as those which are unfrosted. 



The potato may be preserved in a dry state by washing the tubers 

 well in water, then subjecting them to the temporary action of steam, 

 by which the skins are readily detached, and finally slicing them into thin 

 pieces, drying them, and grinding the whole into a powder. Of this, 

 bread may be made by an admixture of wheaten flour or oatmeal. 



Three qualities of potato meal are obtained in grinding, — fine, middle, 

 and black : 1 lb. of bran or refuse is obtained from 12 of meal. 



The manufacturers of potato starch in Germany use a very simple 

 process for determining the qualities of their potatoes. They prepare a 

 solution of salt of a certain density, into which they throw the potatoes ; 

 all those which float are considered too watery to be profitably used in the 

 manufacture of starch, and are rejected. By taking a number of vessels 

 and partially filling them with solutions of salt of different densities, and 

 then successively introducing the roots into one vessel after another, until 

 a solution is found in which they nearly float, we can ascertain in a 

 rough way its relative quality when compared with another root. 



The potato starch, when separated from the pulp and dried, has still a 

 peculiar rank taste, which renders it disagreeable for food. To remove this 

 nauseous odour and taste, it is washed with a weak solution of carbonate of 

 soda, which renders it perfectly sweet. Besides its application in the 

 manufacture of artificial tapioca, sago, vermicelli, &c, it is also used in 

 large quantities in print-works for thickening colours and finishing goods, 

 and also as a substitute for wheaten starch in laundry purposes. The 

 Glenfield Company were the first to introduce a preparation of potato farina 

 having the advantage, when boiled with water, of forming a clear fluid 

 which gives to net and other fine fabrics a transparent appearance, instead 

 of an opaque one. This the Company effects by mixing with the starch a 

 trace of sulphuric acid, which is sufficient to convert the insoluble starch 

 into the soluble substance dextrine. 



(To be continued.) 



