66 HO"W CROPS GEOW. 



Next to water and cellulose, starch is the most abundant 

 ingredient of agricultural plants. 



In the subjoined table are given tlie proportions contained in certain 

 vegetable products, as determined by Dr. Dragendoi-ff. Tbc quantities 

 are, liowever, somewhat variable. Since tbe flguves below mostly refer 

 to air-dry substances, the proportions of bygroscopic w-ater are also 

 given, the quantity of whicli being cbangeable must be taken into ac- 

 count in making any strict comparisons. 



AMOUNT OF STAIiOH XN PLANTS. 



TTata: Starch. 



Per cent. Per cent. 



Wheat 13.3 59.5 



Wheat flour 15.8 68.7 



Eye 11.0 59.7 



oils 11.9 46.6 



Barley 11.5 57.5 



Timothy seed 13.6 45.0 



Eiee (hulled) 13.3 61.7 



Peas.. 5.0 37.3 



Beans (white) 16.7 33.0 



Clover seed 10.8 10.8 



Flaxseed 7.6 33.4 



Mustard seed 8.5 9.9 



Colza seed 5.8 8.6 



Teitow turnips* dry substance 9.8 



Potatoes dry substance 63.5 



Starch is quantitatively estimated by various methods. 



1. In case of potatoes or cereal grains, it may be determined ronghly 

 by direct mechanical separation. For this purpose 5 to 30 grams of the 

 substance are reduced to fine division by grating (potatoes) or by soften- 

 ing in warm water, and crusliing in a mortar (grains). Tlie pulp thus 

 obtained is washed either upon a fine bair-sieve or in a 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 starcli falls out too low, because it is 

 impossible to break open all the minute cells of the substance analyzed. 



3. In many cases starch may be estimated with more precision by con- 

 version into sugar ; see p. 76. 



3. Dr. Dnigondorfif, of the Eostock Labor.atory, proceeds with starch de- 

 terminations as follows: The pulverized substance, after drying out 

 all hygroscopic moisture at 313°, is digested for 18 to 30 hours, at a tem- 

 perature of 313°, in 10 to 13 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. 

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