66 HOW CROPS GROW. 
Next to water and cellulose, starch is the most abundant 
ingredient of agricultural plants. 
In the subjoined table are given the proportions contained in certain 
vegetable products, as determined by Dr. Dragendorff. The quantities 
are, however, somewhat variable. Since the figures below mostly refer 
to air-dry substances, the proportions of hygroscopic water are also 
given, the quantity of which being changeable must be taken into ac- 
count in making any strict comparisons. 
AMOUNT OF STARCH IN PLANTS. 
Water. Starch. 
Per cent. Per cent. 
Wheat: sisi ssiascdes sade 13.2 59.5 
Wheat flour........ ... 15.8 68.7 
TRY Gis vse erste nics ote 664 she apse ote 11.0 59.7 
Oates a: csscassrercsdors 11.9 46.6 
Barley......3.. 11.5 57.5 
Timothy seed. . 12.6 45.0 
Rice (hulled)... 13.3 61.7 
BOOB) sich osiaaae. o's 5.0 87.3 
Beans (white).. ri 16.7 33.0 
Clover seed...... a 10.8 10.8 
Flaxseed......... ets 7.6 23.4 
Mustard seed.... 8.5 9.9 
Colza secd....... 3 5.8 8.6 
Teitow turnips *. .. dry substance 9.8 
Potatoes.......ee06 .. dry substance 62.5 
Starch is quantitatively estimated by various methods. 
1. In case of potatoes or cereal grains, it may be determined roughly 
by direct mechanical separation. For this purpose 5 to 20 grams of the 
substance are reduced to fine division by grating (potatoes) or by soften- 
ing in warm water, and crushing in a mortar (grains). The pulp thus 
obtained is washed either upon a fine hair-sieve or ina bag of muslin, 
until the water runs off clear, The starch is allowed to settle, dried, and 
weighed, The value of this method depends upon the care employed 
in the operations. The amount of starch falls out too low, because it is 
impossible to break open all the minute cells of the substance analyzed. 
2. In many cases starch may be estimated with more precision by con- 
version into sugar; see p. 76. 
3. Dr. Dragendorff, of the Rostock Laboratory, proceeds with starch de- 
terminations as follows: The pulverized substance, after drying out 
all hygroscopic moisture at 212°, is digested for 18 to 30 hours, at a tem- 
perature of 212°, in 10 to 12 times its weight of a solution of 5 to 6 parts 
of hydrate of potash in 94 to 95 parts of anhydrous alcohol. The 
digestion must take place in sealed glass tubes, or in a silver 
vessel which admits of closing perfectly. By this treatment the 
* A sweet and mealy turnip grown on light soils for table use. 
