of food on a small space of ground, but only about 1-7th part of the weight of the tuber is nutritious, and this is chiefly farinaceous. Its farina or starch is, however, accompanied by no inconsiderable portion of saline matter, more especially of potassa, which renders it highly antiscorbutic, and a powerful corrective of the grossness of animal food. When forming part of a mixed diet, perhaps no substance is more wholesome than the potato, and, certainly, no other esculent hitherto discovered appears equally adapted for universal use.
Boussingault gives the following as the average composition of the tubers of the potato:—
| Moist | Dry. | |
| Water | 75·9 | — |
| Albumen | 2·3 | 9·6 |
| Oily matter | 0·2 | 0·8 |
| Fibre | 0·4 | 1·7 |
| Starch | 20·2 | 83·8 |
| Salts | 1·0 | 4·1 |
| ——— | ——— | |
| 100·0 | 100·0 |
Manuring experiments on potatoes in 1867-1869 show that on light soils a mixture of mineral superphosphate, crude potash salts, and ammonium sulphate, produces very beneficial results; on stiff soils nitrogenous manures have little effect. Further proof is given that manuring with common salt tends to decrease the yield.
Analyses, conducted by A. Stockardt, of potatoes grown in eight different years, show that those manured with salt invariably contain less starch than those unmanured, the decrease being from 10 to 20 per cent. of starch; the same effect is produced when the salt is mixed with other manures.
Under the microscope the cells are seen to be very sparingly fitted with starch grains.
Unmanured potatoes contained ·43 per cent. of sodium chloride in the dry substance, and those which had received a small dressing of common salt 1·34 per cent.[121]
[121] Voelcker ‘Roy. Agric. Society’s Journal,’ quoted in ‘Journal of Chemical Society,’ vol. XXV.
No certain rule can be laid down for ‘dressing’ potatoes. “If boiled, it may be that they require to be put into boiling water, or, may be, into cold, and either boiled quickly or slowly; but this you must find out. Choose them all about the same size, with a smooth skin, and when they are boiled and begin to crack, throw off the water immediately, as it only damages the root. When dressed let them stand near the fire, with a cloth over them, and serve them in their skins. Salt may be put into the water at the beginning. A watery potato will require quick boiling, and, sometimes, to be put into boiling water.” (Soyer.)
To retain the highest amount of nourishment in potatoes they should be ‘dressed’ with their skins on them. The bruised or damaged parts, worm-holes, &c., being removed with a knife, the dirt should be carefully cleaned out of the ‘eyes,’ and from the rough parts of the skins, by means of a brush and water, after which they should be well rinsed in clean water, and drained in a colander. If they are at all dry or shrivelled, they may be advantageously left to soak for 3 or 4 hours in clean cold water before cooking them. Potatoes ‘dressed’ in the skins have been found to be nearly twice as rich in potassa salts as those which have been first peeled. The skins are easily removed before sending them to table.