THE WATER OF STARCH. 



167 



Table 15. 



Kind. 



Wheat 



Rye 



Potato 



Corn 



Buckwlieat. 



Rice 



Acorn 



THE W.ATER OF STARCH. 



Starch is very hj^groscopic, and the jier cent of water is variable in relation to temper- 

 ature, the amount of moisture in the air, and the cliaracter and amount of foreign sub- 

 stances present. According to table 14 the percentages range from 12.9 to 19.2 for starches 

 of different kinds, sago starch ha\ing the lowest and preparation a of potato starcli the 

 highest. Payen found that potato starch, after exposure for several days to an atmosphere 

 saturated with moisture, contained 35 per cent of v/ater. The freshly prepared starch may 

 have 45 per cent of water. Soxhlet (Centralb. f. Agrikultur-Chemie, 1S81, 554) recorded 

 for ah'-dried potato starch 20 per cent of water, and for wheat and corn starch IG per cent. 

 Salomon (Jour. f. prakt. Chemie, 1882, xxv, 348; xxvi, 324) gives for air-dried rice starch 

 22.98 per cent of water. Saare (Zeit. Spiritu- 

 siud., 1901, XXIV, 502, 512) found for wheat 

 starch 9.9 to 15.3 per cent (mean 13.2) and 

 about the same for corn. Hoffmann and 

 Philippe (Woch. f. Brauerei, 1905, xxii, 71) 

 give for air-di'ied potato starch 14.38 per 

 cent. According to Dubosc (Dingl. Polyt. 

 Jour., 1892, ccLxxxv, 213) the starch of the 

 sago palm contains 12 per cent of water. Nos- 

 sian (Jour. f. prakt. Chemie, 1861, lxxxiii, 

 41) showed the marked hygroscopic proper- 

 ties of starch by subjecting starches from various sources, that had been dried at 100°, to 

 atmospheres containing 73 and 100 per cent of moisture respectively at 17° to 20° (table 15). 



Archbold (Jour. Soc. Chem. Industry, 1887, vi, 83) gives the following data: 



Starch dried at 100° in vacuo is completely dehydrated. 



Starch dried at 15.5° in vacuo contained 10 per cent of water. 



Starch dried at 20° in air containing 0.0 per cent of moisture contained IS. 6 jier cent of water. 



Starch dried in air .saturated with moisture contained 35.7 per cent of water. 



Carl Nilgeli (Die Starkekorner, etc., loc. cii.) noted that heat is developed upon the 

 addition of water to dry starch. Fischer (Beihefte z. botan. Centralbl., 1902, xii, 227) 

 states that the phenomenon is due to the chemical affinity of the starch-substance for 

 water. Ullik (Zeit. f. d. ges. Brau., 1891, 5G5) dried potato starch at 120° and found that it 

 had contained 12.1 per cent of water. Starch after having been exposed in an atmosphere 

 saturated with moisture at 16° to 20° contained 37 per cent of water, and when mixed 

 with water no rise of temperature occurred. When placed in an indifferent solution, such 

 as a solution of sucrose, anhydrous starch took up 23.75 to 24.58 per cent of water, while 

 the air-dried preparation absorbed from 18.98 to 19.1 per cent. The drier the starch the 

 larger the cjuantity of water taken up and the greater the rise of temperature. Ullik, in 

 experiments with 20-gram quantities of dried starch mixed with the same weight of water, 

 recorded the changes in temperatures shown in table 16. 



Table 16. 



Ullik's results received confirmation in the investigations of Hoffmann and Philippe 

 {loc. cit.) and of Emslander and Freulich (quoted by Hoffmann and Philippe). 



