442 VEGETABLE SUBSTANCES. 



to combine with his own regular business, the some 

 what anomalous calling of a swine-keeper. 



Starch is found in the greater number, if not in the 

 whole of the seeds employed as articles of food. A 

 large proportion is extracted from potatoes, about 

 five pounds of these roots yielding one pound of 

 starch. 



If starch be placed in shallow pans within an oven, 

 and exposed to a heat of about 600, it swells consi- 

 derably, becomes soft, and exhales a very powerful 

 smell, first changing to a yellow and afterwards to a 

 cinnamon colour. By this treatment starch loses all 

 its amylaceous properties, and acquires those of gum; 

 it is now soluble in cold water, and in this state is 

 much used by calico-printers, as being in many re- 

 spects an efficient substitute for foreign gum. 



Many attempts have been made to draw from other 

 sources of home production some mucilaginous sub* 

 stance, which might be applied to topical dyeing. 

 Some of these substitutes have been advantageously, 

 though not very generally, employed in different parts 

 of the United Kingdom. 



All the indigenous species of lichens contain a con- 

 siderable portion of viscid matter, and this has been 

 successfully converted into a gum, possessing all the 

 properties of gum arabic or Senegal. The lichens 

 applicable to the purpose are generally found on trees 

 growing on poor stiff soils. They attain to maturity 

 in three or four years, so that a crop may be taken 

 from the same tree every fourth year. Immediately 

 under the external skin is a green resinous substance ; 

 the remainder is composed partly of gum, and partly 

 of a fibrous matter, which is insoluble by the action 

 of heat or of the alkalis. 



To obtain the viscid matter, the lichen is scalded 

 two or three times in boiling water ; this separates 



