104 



DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Table 5. 



Table 6. 



In another inquiry, Fouard (Compt. rend., 1908, cxlvii, 931) investigated the altera- 

 tions which occur in the pseudo-sohition upon standing. A neutral pseudo-.sohition con- 

 taining 54.3 grams of starch per hter at 15° was studied by removing portions at definite 

 intervals ranging from a few hours to many days, filtering 

 through collodion membranes, and determining the amounts 

 of solitl matter and the specific rotatory powers. The prepa- 

 rations, he found, undergo spontaneous gelatinization, and 

 the process goes on during a period of several months. The 

 results of these experiments, Fouard records, confii-ms his 

 former view of starch existing in different states of molecu- 

 lar aggregation, each state having a definite and specific 

 rotatory power. During the process of gelatinization the 

 collodion membrane transmits these different aggregates in 

 definite order, the first to be checked being the most active 

 polariscopically. The results of this series of experiments 

 are shown in table 5. 



The rotatory power of the filtrates remained constant. 

 In another series of experiments a similar pseudo-solution 

 kept at 20° was filtered during a period of 126 hours, and 

 samples taken after the lapse of (5, 30, 78, and 126 hours, 

 respectively, with the results shown in table 6. 



The residual colloidal starch gelatinized on the filter 

 during the sixth day, owing to concentration of the solution, 



causing the amount of starch in the filtrate to fall rapidly. In another inquiry, Fouard 

 (Compt. rend., 1909, cxlvii, 502) found that the specific rotatory power of true solution 

 of starch was reduced by the addition of small quantities of potassium hydrate, the larger the 

 quantity of alkali the greater the effect, the rotatory power falling as low as {a)j) =141. 

 Neutrahzation instantly reverses the modification. He made further observations on the 

 fractions obtained from pseudo-solutions at different stages of spontaneous gelatinization, 

 and noted that as gelatinization advances the specific rotatory power of the dissolved 

 starch falls towards the level of the rotatory power of maltose. He believes that the solu- 

 tion of starch, whether by water or by the action of potassium hydi-ate, depends upon a 

 reversible hydrolysis, with maltose as its ultimate term. Therefore, starch is simplj' a 

 molecular aggregate of maltose in variable and unknown form. He concludes that no 

 chemical combination takes place between the starch and alkali, that starch has not acid 

 functions, and that the action is essentially ionic. The presence of perfectly soluble starch 

 in solution lowered the conductivity of the solution, but to a )nuch less extent in the 

 presence of anmionia than potassium. Before coagulation occurs, association of the starch 

 with metalUc ions is beUeved by him to take place. 



The use of dilute acids to cause a reduction of starch-grain or starch-paste to soluble 

 starch, or to render raw starch more soluble in cold water, was adopted by a number 

 of the earlier investigators, but it is probable that Bechamp (Compt. rend., 1854, xxxix, 

 653; 1856, xlii, 1210) was the first to use this method to obtain soluble starch, which 

 substance he regarded as a special body occurring between common starch and dextrin. 

 Since that time this method, and also various modifications of it, have been in continuous 

 use, and no one, it seems, has so popularized it as Lintner (Jour. f. prakt. Chemie, 1886, 

 XXXIV, 378), as is indicated by the comparatively very frequent references to " Lintner 's 

 soluble starch." His method is given as follows : Mix some good potato starch with enough 

 7.5 per cent hydrochloric acid to cover the starch. Allow this to stand at ordinary room 

 temperature for 7 days, or for 3 days at 40°, when the starch will have lost its gelatinizing 

 property. Decant with cold water until sensitive litmus paper shows no acid reaction, 



