THE VOLATILE PART OF PLANTS. 53 



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 grat ing (potatoes) or by sof- 

 tening in warm water, and crushing in a mortar (grains). The pulp 

 thus obtained is washed either upon a fine hair-sieve or in a bag of 

 muslin, until the water runs off clear. The starch is allowed to settle, 

 is 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 sub- 

 stance analyzed. 



2. In many cases starch may be estimated with great precision by 

 conversion into sugar. For this purpose Sachsse heats 3 grams of air- 

 dry substance, contained in a flask with reflux condenser, in a boiling 

 water bath for 3 hours, with 200 c. c. of water and 20 c. c. of a 25 per cent 

 hydrochloric acid. After cooling, the acid is nearly neutralized with 

 sodium hydroxide, and the dextrose into which the starch has been con- 

 verted is determined by Allihn's method, described on p. 65. Winton, 

 Report Ct. Ag. Exp. St., 1887, p. 132. 



3. For Dragendorff's method, see Henneberg's Journal, fur Lancl- 

 wirthschaft, 1862, p. 206. 



Amidulin, or Soluble Starch. A substance soluble 

 in cold water appears to exist in small quantity in the in- 

 terior of ordinary starch-grains. It is not extracted by 

 cold water from the unbroken starch, as shown by Exp. 

 26. On pulverizing starch-grains under cold water by 

 rubbing in a mortar with sharp sand, the water, made 

 clear by standing or filtration, gives with iodine the char- 

 acteristic blue coloration. Exp. 27 shows that when 

 starch is gelatinized by hot water, as in making starch 

 paste, a small quantity of starch goes into actual solu- 

 tion. 



Ordinary insoluble starch may be largely converted 

 into soluble starch by moderate heating, either for a long 

 time to the temperature of boiling water or for a short 

 space to 375 F. Maschke obtained a perfectly clear solu- 

 tion of potato-starch by heating it with 30 times its bulk 

 of water in a sealed glass tube kept immersed for 8 days 

 in boiling water. Zulkowski reached the same result by 

 heating potato-starch (1 part) with commercial glycerine 

 (16 parts). In this case the starch at first swells and 

 the mixture acquires a pasty consistence^ but, when the 



