100 THE POTATO AND ITS COMMERCIAL PRODUCTS. 



notwithstanding which the raw feeula gives a blue colour when treated 

 with iodine, and the calcined a purple. 



The colour of calcined farina is an objection to its employment in many 

 instances ; but it has now been found that any amylaceous substance may 

 be converted into soluble dextrine without any change of colour, by sub- 

 jecting it to the chemical action of muriatic 6v other acid gas or vapour in 

 a cylinder, the exterior of which is surrounded by an atmosphere of steam. 



Under the name of polenta, in France, a large manufacture is carried on 

 of potatoes, which are boiled or steamed, and peeled, and then passed 

 through a pair of fluted cylinders, then bruised, and bolted or sifted 

 through a searce or sieve, and separated into coarse grains, semola, or 

 flour. If stored in a dry place, polenta may be kept a long time good. It 

 is used for thickening soups, and making other food-dishes with eggs, milk, 

 meat, or pulse. Potato-starch is known in French commerce asfecule; as 

 usually met with, it contains from 18 to 25 per cent, of water. If we stir 

 a parcel of fecule containing 20 per cent, of water, it makes a crackling 

 noise, which is a characteristic of dryness to the dealers ; and that which 

 contains 25 per cent, of water will mostly be deficient in this crisp test, for 

 if crushed between the fingers it will adhere or form a lump. 



Good, wholesome bread may be made by mixing the starch with the 

 dried pulp of peasmeal, beanmeal, oatmeal, or flour. On the Continent, the 

 farina is largely used for culinary purposes. The famed gravies, sauces, 

 and soups of France are indebted for their excellence to that source ; and its 

 bread and pastry equally so. The starch of potatoes, like all other kinds 

 of starch, is unfit alone for the preparation of pastry; but a small proportion 

 of potatoes, or of potato-starch, added to wheaten flour, is considered by 

 some to improve the quality of bread. If the proportion of potato-starch 

 exceeds one-fifth of the weight of the flour, a peculiar flavour is communi- 

 cated to the bread, arising from a minute quantity of an oily matter con- 

 tained in several amylaceous principles, which is supposed by M. Payen 

 to be identical with the oil of potato -spirit, or fusel oiL This substance 

 was discovered by Scheele in brandy obtained by distilling fermented 

 potatoes. It is a colourless, oily liquid, possessing a very powerful odour, 

 at first rather agreeable, but immediately afterwards nauseous in the 

 highest degree. This substance is generally believed to be a product of 

 the fermentation of the potato, and not to pre-exist in the tuber. If potato- 

 starch is washed first with tasteless alcohol, and afterwards with cold water, 

 it may be entirely deprived of its peculiar flavour, and loses in weight, 

 at the same time, about one part in 2,000. 



Some years since, grape-sugar or glucose used to be largely prepared 

 in this country from potato-flour ; and as it was sold much under the price 

 ■of cane-sugar, it found a ready sale, grocers employing it for the purpose 

 of adulteration. The Excise authorities becoming acquainted with the 

 fact of the extensive manufacture of potato-sugar, imposed a duty upon it, 

 since which I believe it has ceased to be prepared. 



