THE REACTION OF STARCHES. 



169 



THE REACTION OP STARCHES. 



The reactions of commercial starches differ wadely, owing chiefly to different methods 

 of preparation and variable contaminations. Soxhlet (Reportorium f. analyt. Chemie, 

 1881; Jahr. ii. d. Fort. d. Thierchemie, 1881, xr, 86), by titrating commercial starches 

 wdth a standard solution of sodium hydroxide, determined that for every 100 grams of 

 potato or wheat starch the acidity was equal to O.OG to 0.4 gram of sulphuric acid. For 

 potato starch from 15 to 85 c.c. of a N/lO NaOH solution, and for wheat starch from 13 

 to 19 c.c. were required for neutralization. Rice and corn starches were, on the other hand, 

 usually markedly alkaline. 



Meyer (Die Stiirkekorner, loc. cil.) states that the reaction of commercial starches 

 varies, generally being acid, but sometimes alkaline. He I'ecords that he has not found a 

 neutral preparation. Saare (Zeit. Spiritusind, 1901, xxiv, 502) noted that both wheat and 

 corn starches are acid, wheat being the more acid. 



Ford (Jour. Soc. Chem. Ind., 1904, xxiii, 414) observed that the reactions of starch 

 preparations, as determined by color indicators, are variable in accordance with the indi- 

 cator. A solution of ordinary starch may be neutral to rosolic acid, acid to phenol- 

 pthaleine, and alkaline to methyl orange. Therefore, in referring to starch as being 

 neutral, acid, or alkaline, it is necessary to define in what sense the word is used. Litmus 

 paper and litmus solution, he states, 



are useless for testing starch. A Table 17. 



number of starches from different 

 sources were prepared bj' succes- 

 sive treatment with alkali and di- 

 lute acid, well-washed, and dried. 

 Given quantities (15 to 20 grams) 

 were gelatinized by heat, and upon 

 cooling were liquefied at 79 to 80 by 

 a trace of precipitated diastase, and 

 then boiled. The preparation was 



made up to 500 c.c, then 1 c.c. of malt extract was added to each 70 c.c. of prepara- 

 tion and the mixture digested at 40 for an hour, and then boiled and made up to 100 c.c. 

 The reactions of 10 grams of preparation were found to be as given in table 17. 



From similar preparations of the same starches made by Lintner's method, the results 

 appearing in table 18 were recorded. 



Table 18. 



The acid property of starch was noted by Blondeau (Compt. rend., 1864, lix, 403), 

 who states that starch forms with ammonia a combination having the projierties of a 

 weak base. Rice starch demineralized by dilute hydrochloric acid and washed free from 

 acid was found by Demoussy (Compt. rend., 1906, cxlii, 933) to have properties of a 

 weak acid comparable to carbonic acid. He reports that it forms compounds with metallic 

 hj'droxides, ammonia, and alkaline carbonates which are dissociable b}' water. He also 



