172 



DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



PHENOLS WITH SULPHURIC OR HYDROCHLORIC ACID. 



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

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

 sulphuric or hydi-ochloric acid give with carbohych-ates 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 diffei'ent 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 solution of this substance and hydrochloric acid, a 

 fine cherry-red is produced. 



REACTKlXS 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 given 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 hydroxide, tannin, sulphuric and other 

 mineral acids, acetic acid, concentrated solution of chloride of zinc, glj'cerine, etc., were 

 used by the investigators prior to the seventies in studying the properties of starch-grains. 

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

 to iiring out the microchemical properties of a-amylose, /3-amylose, and amlylodextrin, 

 including among these potassium hydroxide, calcium nitrate, 25 per cent hych-ochloric 

 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+iodine solution (equal parts of each). 



2. Chlor-zinc-iodide solution. 



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



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

 saturation). 



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 first uniformly blue in color; swelling of 

 the grains soon takes place and finally alternate light 

 blue and blue layers are observed. 



(2) Chlor-zine-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 iiot 

 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 

 fissui'es or i)oint of growth, whirli is in marked contrast 

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

 grains swell at one end, the portion showing the .swelling 

 becomes light Ijlue, and finally almost colorless, while 

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

 the grains finally disintegrate into several portions. 



