[ 69 ] 



This estimation agrees very nearly with the definite 

 proportions of 11 of carbon, 1O of oxygene, and 20 

 of hydrogene. 



All the varieties of gum and mucilage are nutri- 

 tious as food. They either partially or wholly lose 

 their solubility in water by being exposed to a heat 

 of 500 or 600 Fahrenheit, but their nutritive powers 

 are not destroyed unless they are decomposed. Gum 

 and mucilage are employed in some of the arts, parti- 

 cularly in calico-printing : till lately, in this country, 

 the calico-printers used gum arabic \ but many of 

 them, at the suggestion of Lord Dundonald, now 

 employ the mucilage from lichens. 



2. Starch is procured from different vegetables, 

 but particularly from wheat or from potatoes. To 

 make starch from wheat, the grain is steeped in cold 

 water till it becomes soft, and yields a milky juice by 

 pressure ; it is then put into sacks of linen, and pres- 

 sed in a vat filled with water : as long as any milky 

 juice exudes the pressure is continued ; the fluid 

 gradually becomes clear, and a white powder subsides, 

 which is starch. 



Starch is soluble in boiling water, but not in 

 cold water, nor in spirits of wine. According to 

 Dr. Thomson, it is a characteristic property of starch 

 to be soluble in a warm infusion of nutgalls, and to 

 form a precipitate when the infusion cools. 



Starch is more readily combustible than gum ; 

 when thrown upon red hot iron, it burns with a kind 

 of explosion, and scarcely any residuum remains. 



