126 THE BOOK OF NATURE STUDY 



is water. To determine this amount very roughly, a very thin 

 slice of potato, apple, radish, etc. may be weighed on the ordinary 

 balance used in schools for elementary chemical and physical 

 determinations. The slice is then strung on a knitting needle 

 and placed in an air oven maintained at a temperature of about 

 110 for some hours. A very great decrease in weight owing 

 to loss of water will be observed. The results may be compared 

 with those obtained similarly in the case of slices of Brazil nuts 

 or chestnuts. The results, though rough, will sufficiently indicate 

 the difference in water contents. Nuts and seeds contain from i 

 to 10 per cent, of water, while juicy fruits and vegetables contain 

 from 50 up to over 90 per cent. 



Of the carbohydrates, starch is present to the extent of 10 

 to 14 per cent, in Potatoes, while sugars are present to about 

 the same amount in ripe Apples, Pears, Grapes, Strawberries, and 

 Raspberries. Parsnips and Carrots contain 6 to 10 per cent, 

 of sugar, and Sugar Beet contains 15 per cent. To show the 

 presence of starch, peel a potato, and then grate it on a nutmeg 

 grater, allowing the grated portion to fall on a piece of fine 

 muslin stretched over a glass jar or jug. By washing the grated 

 mass with water the starch grains are carried through into the 

 glass vessel, while the cellulose remains on the muslin as a soft 

 whitish mass. If the starch is allowed to settle and the liquid 

 decanted the finely granular character of starch can be easily 

 made out. Starch grains from various vegetables may be 

 examined under the microscope and their appearance compared. 



Sugars can, of course, be detected in ripe fruit by the taste, 

 and their presence demonstrated chemically by warming a little 

 of the filtered expressed juice with Fehling's solution. Crystals 

 of sugar may also be obtained by boiling Carrots, Parsnips, or 

 Sugar Beet in water, crushing the boiled mass, filtering, and 

 evaporating the filtrate to small bulk. 



The presence of oil in nuts is best shown by means of thin 

 sections mounted in water and examined under the microscope. 

 Or we may imitate the process of manufacture of agricultural 

 " oilcake," by crushing seeds of rape or of flax, which contain 

 30 to 40 per cent, of oil. Many of the proteid substances of plants 

 are soluble in water, and like white of eggs are coagulable by heat. 



