302 VINEGAR, CIDER, AND FRUIT-WINES. 



insoluble ; by long boiling in water, by pectase, or by an excess 

 of alcohol it is soon transformed into pectic acid. 



By allowing pectase to act for some time upon pectine, pectic 

 acid is formed ; the same conversion taking place almost instan- 

 taneously by dilute solution of potash, soda, ammonia, alkaline 

 carbonates, as well as by barium, lime, and strontium water. Its 

 formation in the above-described manner is preceded by that of 

 pectosic acid, which, as previously mentioned, is converted by the 

 same agents into pectic acid. 



Pectic acid is insoluble in cold, and scarcely soluble in hot, 

 water; by boiling it, however, for a certain time in water, and 

 constantly replacing the water lost by evaporation, it disappears 

 entirely, and is converted into a new acid soluble in water. By 

 nitric acid it is transformed into oxalic acid and muric acid ; 

 alkalies decompose it very rapidly, the final result being metapec- 

 tic acid, which is soluble in water, but non-crystallizable ; on 

 boiling in hot water, the solution forms a jelly after cooling. 



Pectic acid further possesses the special property of dissolving 

 in a large number of alkaline salts and forming with them true 

 double salts which always show a decidedly acid reaction, dissolve 

 in water, and on cooling form consistent jellies. 



By boiling for a few hours a solution of a pectous salt, the latter 

 is transformed into a parapectous salt which, when decomposed 

 by a dilute acid, yields parapectic acid. It is non-crystallizable, 

 shows a strong acid reaction, and forms soluble salts with alkalies ; 

 it is precipitated by barium water in excess. 



Metapectic acid is formed in various ways, among others by 

 leaving an aqueous solution of parapectic acid to itself for some 

 time, but also by the action of the lime contained in the cell-tissue 

 of roots and fruits upon pectose. It is insoluble in water, does not 

 crystallize, and gives soluble salts with all bases. With an excess 

 of bases the salts acquire a yellow coloration ; they are precipi- 

 tated by basic lead acetate. 



What has been said in the preceding may be briefly condensed 

 as follows : 



1. By the influence of heat upon pectose pectine is formed. 



2. Pectine is transformed into parapectine by boiling its aque- 

 ous solution for several hours. 



