150 VEGETABLE PRODUCTS. 



closely allied substance, is afforded by the Malvaceae and from 

 Flax-seed, Arc. Bassorin, an insoluble gum, exists in the Gum 

 Tragacantb, which exudes from species of the Astragalus. This 

 ipsoluble substance is called by some vegetable gluten, and differs 

 from Arabin in containing phosphate of lime. By digesting it 

 in muriatic acid it becomes completely soluble, and pure gum is 

 precipitated by alcohol. 



289. Gum enters largely into our food, in the form especially 

 of dextrine, into which starch is converted by cooking. It is 

 employed largely in the arts, especially in manufactories of cloth 

 and calico printing. In medicine it is extensively employed as 

 a medium for the administration of medicines, and as a de- 

 mulcent for covering inflamed surfaces, and blunting the action 

 of acrid secretions. Lozenges, Pastiles, and Gum Pastes, are 

 frequently formed mostly of gum and sugar. 



290. Pectin, C 64 , H 40 , 56 + 8 HO, is a substance undergoing 

 various changes, and possessing various properties. The char- 

 acteristic property is, that it will form jelly with water. It occurs 

 in almost all plants, especially in the fruits of the Pomaceae, in 

 oranges, lemons, tamarinds, <fcc. 



The material first formed in the plant is an insoluble sub- 

 stance, pectose, so closely connected with cellulose as not to be 

 separated from it without change. It exists only in quite un- 

 ripe fruits, together with a substance called pectase, which acts 

 upon it, converting it into pectin as the fruit ripens. Pectin is 

 soluble in water, but insoluble in alcohol. The still continued 

 action of pectase forms pectosic acid, which is slightly soluble in 

 cold water, but soluble in boiling water. Boiling converts this 

 acid into Pectic acid, which is insoluble in water, and forms our 

 vegetable jellies : alkalies, or pectosic acid, does the same. Too 

 long boiling converts pectic acid into parapectic or metapectic, 

 neither of which form jellies. These are the substances formed 

 when the housewife does not succeed in making jellies. 



291. Sugar. There are several varieties of saccharine sub- 

 stances found in plants, which differ more or less in properties, 

 and even in their chemical constitution. 



Cane-sugar, ( ' .. 1 1. . ( >, n . This variety is found especially in 

 the Sugar-cane, Sugar-maple, and Beet. From these plants it is 

 obtained for commercial purposes. It is in solution in the cells 



What is l>a>s«.r'm ] How <1<h's it differ from arabin ?— 289. How employed 



in the nits' How in medioine \ — 290. Constitution of pectine! Its ohar- 



ticproperty? Where mosth occur? What is peotose? Whereonty 



How converted into peotin? Properties oi pectin! What next 



converted into 1 What does boiling do ? Whatdoesit form! What effect 



of too long boiling I — 291. Constitution of cane-sugar I Whence obtained? 



