108 CROPS 



I. CROP CONSTITUENTS AND THEIR DETERMINATION 



91. Water or Moisture. — This is the loss in weight of the 

 material which takes place when it is dried at the temperature 

 of boiling water, a little under 100° C. usually, and in an 

 atmosphere of hydrogen or in vacuo. If the temperature 

 is lower, not all of the water will be driven off; if it is higher, 

 organic compounds begin to break up and the results will 

 be high. It is necessary to make the determination in an 

 atmosphere of hydrogen or in vacuo, because many crops 

 contain "drying" or "semidrying" oils, which would absorb 

 oxygen if dried in the air, and the results for moisture would 

 be incorrect. 



92. Crude Fat. — This constituent is obtained by extracting 

 the dried material with dry, alcohol-free ether. The extract 

 is dried carefully at the temperature of boiling water to 

 remove the ether, and then weighed. If water is present 

 in the sample, or if. it is present in the ether, or if alcohol 

 is present in the ether, there is danger of dissolving some 

 of the carbohydrates and ash constituents. Crude fat 

 consists of fixed oils, volatile oils, waxes, resins, chlorophyl, 

 and other pigments, if present, and possibly some other 

 ether-soluble compounds. This accounts for the fact that 

 it is called crude fat, for it is an approximate method at best, 

 although in most of our crop plants the constituents other 

 than fixed oils are very small in amount. 



93. Crude Fiber. — The material which has been dried and 

 extracted with ether is boiled first with dilute sulphuric 

 acid, then with dilute sodium hydroxide with a thorough 

 washing after each treatment. The amount of acid and 

 alkali, as well as the strength and time of boiling are very 

 carefully regulated. By drying and weighing the residue, 

 igniting and weighing the remaining ash, the difference in 

 weight will give the crude fiber which consists of cellulose, 

 lignin, and possibly some proteins. The treatment with 

 acid and alkali is supposed to remove all soluble sugars; 

 starch which is hydrolyzed to dextrose and washed out; 

 proteins which are hydrolyzed and removed; and any other 

 constituents rendered soluble by these reagents. 



