24 CHEMISTRY AND USES OF THE POTATOE. 



(85.) The starch of the potatoe is used in the arts for 

 various purposes. " To extract it the potatoe should be 

 grated fine (a piece of iron pierced with holes makes a 

 good grater), and on a first attempt I found that 10 Ib. 

 weight will be grated by a boy in twenty-five minutes. 

 A crushing machine would be preferable where large 

 quantities have to be treated. The pulp should be 

 thoroughly washed in water, and the whole strained 

 through a very fine sieve several times, when the starch 

 and soluble matters will pass through ; and after standing 

 a short time, the starch, by its superior weight, falls to the 

 bottom. The separated liquor should be poured off, and the 

 starch mixed successively with several quantities of water 

 till the water becomes quite tasteless. The starch should 

 then be dried in a warm room, and thus prepared will keep 

 for a long period." 



(86.) Various machines have been contrived for per- 

 forming the operation of rasping potatoes with rapidity, one 

 of which, invented by St. Etienne, is said to be capable of 

 preparing eighteen cwt. per hour. 



(87.) The starch is much used in the preparation of 

 calicoes, but every judicious housewife will buy that 

 unstarched. To detect starch in calico, apply a drop of 

 solution of iodine in iodide of potassium ; this shows the 

 presence of starch by striking a deep blue color. 



(88.) Potatoe starch is often sold under the name of 

 English arrow-root, and is probably often sold for the true 

 arrow-root, being applicable to the same purposes. Accord- 

 ing to Christison it is more apt to cause acidity. It is used 

 by the cook in the preparation of souffles, and sometimes as 

 a substitute for wheat flour in thickening sauces, &c., on 

 account of its being both cheap and tasteless. 



