172 



niFFERENTTATION AND RPKCIFICITY OF STARCHES. 



PHENOLS WITH SULPHUUIC OK HVDKOCHLOKIC ACID. 



It was found by Ihl (Chem. Zeit., 1887, xi, 19; Zeit. d. Alpiiien. Oesterr. Apotheker- 

 Vereiiis, 18SS; Jour. Soc. Chem. Ind., 1887, vi, 306, and 1888, vii, 511) that phenols with 

 sulphuric or hydrochloric acid give with carbohydrates brilliant color reactions. If starch 

 be moistened on a watch-glass with an alcoholic a-napthol solution, and if then a few drops 

 of warm sulphuric acid are added, the starch is colored red-violet. Thymol, cresol, guaiacol, 

 and pyrocatecol produce a splendid vermilion-red; resorcinol and orcinol give a yellow- 

 red; whereas phloroglucinol gives a yellow-brown. The different kinds of gum behave on 

 the whole like starch. The actions of phloroglucinol on arabin is very characteristic. If 

 arabinose be boiled with an alcoholic sokition of this substance and hj-drochloric acid, a 

 fine cherry-red is produced. 



REACTIONS WITH ANILINE DYES. 



Starch seems to have affinities for many aniline dyes. Investigations in this connec- 

 tion have been referred to particularly on pages 55 to 58, and sufficient has been shown to 

 prove that starch from different sources and even parts of the same grain do not react 

 identically with a gi\'en stain. 



REACTIONS WITH VARIOUS AGENTS, WITH ESPECIAL REFERENCE TO THE DEMONSTRATION OF 

 THE STRUCTURE AND COMPOSITION OF THE STARCHES FROM DIFFERENT SOURCES. 



Quite a number of reagents, such as potassium hj'droxide, tannin, sulphiu'ic and other 

 minei'al acids, acetic acid, concentrated solution of chloride of zinc, glycerine, etc., were 

 used b}^ the investigators prior to the seventies in studying the properties of starch-grains. 

 Meyer (Die Starkekorner, loc. cit.) made use of a niunber of such reagents besides enzymes, 

 to bring out the microchemical properties of a-amylose, j3-amylose, and amlylodextrin, 

 including among these potassium hydroxide, calcium nitrate, 25 per cent hj^lrochloric 

 acid, and 3 per cent acetic acid. Kraemer (Jour. Amer. Chem. Soc, 1899, xxi, 650; Amer. 

 Jour. Pharm., 1899, 174; Botanical Gazette, 1902, xxxiv, 341) made a comparative study 

 of the structure of wheat, corn, and potato starches by means of the following agents: 



1. Choral-iodine-j-iodine solution (equal parts of each). 



2. Chlor-zine-iodide solution. 



3. Chloral solution (saturated), water, and glycerine 



(equal parts of each, to which iodine is added to 

 satui'ation). 



4. Calcium nitrate solution, 30 per cent. 



5. Chromic acid solution, 15 per cent. 



6. Saliva. 



7. Taka-diastase. 



8. Silver nitrate solution, 2 per cent. 



9. Sulphuric acid, C. P. with 10 per cent of water. 



10. Sodium acetate solution, 50 per cent. 



11. Potassium hydroxide solution, 0.1 per cent. 



12. Potassium nitrate solution, saturated. 



13. Potassium phosphate solution, saturated. 



14. Tannin solution. 



15. Hydrochloric acid, 5 per cent. 



16. Water. 



The results of his comparative study of wheat and corn starch are presented in the 

 following quotation: 



Wheat. 



(1) Chloral-iodine + iodine solution causes the grains 

 to become at fii-st uniformly blue in color; swelling of 

 the grains soon takes place and finally alternate light 

 blue and blue layers are observed. 



(2) Chlor-zinc-iodine behaves .similarly to the pre- 

 ceding reagent. 



Corn. 



(1) Chloral-iodine +iodine solution causes some of 

 the grains to swell in 5 hours and others to show a 

 tricheten arrangement of the layers; the grains do not 

 appear to be swollen to the extent that the wheat grains 

 are, and therefore show apparently a deeper color with 

 the iodine. 



(2) Chlor-zinc-iodide brings out immediately the 

 fissures or point of growth, which is in marked contrast 

 to the wheat starch; in the course of several hours the 

 grains swell at one end, the portion sho\\ing the swelling 

 becomes light blue, and finallj' almost colorless, while 

 the other portion remains of a deep blue color; some of 

 the grains finally disintegrate into several jiortions. 



