68 STUDIES ON APPLES. 



herbaceous plants, in the cortical layers of trees, and in fruits. So con- 

 stant was its occurrence in his researches that this author regarded 

 it as one of the principal constituents of all plants. He considered it 

 to be similar, if not entirely identical, with the principle in plants 

 vaguely described as jelly. The method given by Braconnot for 

 obtaining pectin (as pectic acid) from roots containing starch is to 

 pulp the roots, wash out with water to remove sugar, then boil the 

 marc with dilute hydrochloric acid, wash, and heat the starch-free and 

 sugar-free marc with very dilute potash or soda. There results a 

 mucilaginous slightly alkaline liquid, from which hydrochloric acid 

 separates pectic acid as a jelly. So prepared, pectic acid had a feebly 

 acid reaction to litmus and was slightly soluble in hot water, but the 

 filtered liquor did not precipitate on cooling, and barely reddened 

 litmus. It was, however, coagulated by alcohol, by metallic salts, and 

 even by sugar. Dried on a capsule it appeared as transparent leaflets 

 which loosened from the capsule as they dried. These were slightly 

 swelled by cold water, and dissolved slightly in boiling water. A 

 potassium salt was separated by precipitating its water solution with 

 alcohol, excess of alcohol extracting coloring matter and excess of 

 alkali. This salt was very soluble in water, possessed a flat insipid 

 taste, and yielded 15 per cent of potassium, calculated from the sul- 

 phated asft. Its water solution was coagulated by salts, and by alcohol 

 and sugar, and gave precipitates with solutions of salts of heavy 

 metals. An ammonium salt was prepared which possessed properties 

 similar to those of the potassium salt. The use of these salts for the 

 preparation of jellies was suggested, and experiments are described in 

 which beautiful jellies were obtained. 



The pectic acid was attacked only slightly by concentrated sulphuric 

 acid in the cold. Nitric acid yielded oxalic acid and a white powder 

 which was treated with ammonia to separate from calcium oxalate. 

 The ammonia solution, acidulated, gave a granular crystalline sub- 

 stance which he believed to be mucic acid. Braconnot concluded the 

 article .by proposing for this acid the name pectin, from the Greek 

 word 7T7//crk, meaning coagulum. 



Vauquelin" worked on the carrot, obtaining pectin from the juice 

 by boiling in order to clarify, then precipitating with alcohol; and 

 from the marc (as pectic acid) by boiling with dilute caustic potash and 

 precipitating with calcium chlorid, or better, barium hydroxid, filter- 

 ing, treating the filtrate with sulphuric acid, and then with potassium 

 hydroxid, finally precipitating with hydrochloric acid. Distilled or 

 filtered rain water is stated to be necessary. 



Braconnot* in 1833 described the pectin separated from oak bark by 

 solution in alkali. It was not precipitated from solution in alkali by 



Anri. chim. phys., 1829 [2], 41: 46. 

 &Ann. Chem. (Liebig), 1833, 5: 275. 



