THE POTATO AND ITS COMMERCIAL PRODUCTS. 339- 



2nd. From 81b. of peeled tubers — 







Amyluin, or starch - - - - - 



- 



1 3 



Peelings ____.- 



- 



1 5 



Pulp, pressed ------ 



- 



1 14 



Loss _ . . . - 



- 



3 10 



Thus the yield of starch was decreased by peeling ; 



whence he inferred 



that potatoes should be cleaned by brushing under water, and then boiled 

 unpeeled — or, as we say, " in their jackets." 



Pure starch of the potato, in common with Indian arrowroot, is nearly 

 allied to sugar ; and by not containing azote, or nitrogen, cannot nourish 

 and support animal muscular tissue. Hence, however starch and sugar 

 may tend to produce fat, and to sustain the respiratory processes, we cannot 

 consider either of them calculated to build up and support the human 

 frame. 



The shoots of germinating potatoes contain a small quantity of sola- 

 nine, an extremely poisonous substance, which constitutes the active 

 ingredient of the deadly nightshade, another of the Solanums. The germs 

 developed in the spring contain a very sensible quantity of this poisonous 

 principle. The tuber itself sometimes contains a small quantity, which it 

 readily yields to water. If germinated potatoes (with the germs remaining) 

 are employed in the preparation of potato spirit, the residue contains so 

 large a quantity of solanine, that cattle fed with it become paralysed in 

 their posterior extremities. This is by no means a rare instance of the 

 contiguity of an active poison and an amylaceous substance. In the tuber 

 of Arum maculatum, for instance, from which Portland arrowroot is made, 

 starch is associated with an acrid principle which gives it a purgative pro- 

 perty ; and in the root of the bitter cassava (Janipha Manihot), from 

 which the Brazilian tapioca and cassava meal are prepared, the starch is 

 accompanied by hydrocyanic acid. But, fortunately, the poisonous matters 

 may always be removed by extremely simple means. They are invariably 

 soluble with facility in water ; hence the process of washing in cold water 

 suffices for their removal. 



In the West Indies^ and Demerara, the cassava starch is exposed to a 

 moderate heat, when the prussic acid, which is extremely volatile, is 

 entirely dissipated in vapour, and the concentrated watery extract, previ- 

 ously poisonous under the name of " cassareep," forms a condiment and 

 seasoning of the flavour of soy, which, from its antiseptic properties, is the 

 basis of the well-known negro mess termed " pepper-pot." 



Potato starch may be known from true arrowroot by rubbing a little of 

 it between the finger and the thumb, when it will be observed that the 

 potato starch is softer to the touch and more shining to the siglit than 

 arrowroot. The microscope is, however, the most important agent in 

 distinguishing the different starches from each other, and by it we can 

 readily detect potato starch. We recognise it by the size, shape, and 

 structure of its grains, and the numerous concentric rings visible on its 

 surface. Though the size varies somewhat, yet on the average it exceeds 

 that of other commercial starches, always excepting tons les mois, whose 



