NEUTRAL SUBSTANCES. 125 



jeoted to pressure, and a juice extracted, which yields it in the 

 greatest abundance. It is a fine white powder, destitute of 

 taste and smell, and very much resembles starch. 



Lignin (Ci5H'OOio=180.) This name is given to the fi- 

 brous portions of wood, which remain after digesting common 

 wood in water, muriatic acid and alkalies. It constitutes the 

 skeleton of the trunk and branches of trees. The quantity of 

 lignin varies in different kinds of wood, but generally there are 

 96 parts in 100. Sulphuric acid converts it into sugar, and 

 potash into ulmin. It is the substance which remains, when 

 wood is converted into charcoal, or rather it is the lignin which 

 is converted into charcoal by heat. It may be made into ex- 

 cellent bread. The inner bark of flax and hemp, and the 

 fibres of cotton, are probably the same substance. It is by far 

 the^ most abundant substance in vegetables. 



Fimgin is a peculiar vegetable principle derived from mush- 

 rooms, and approaches in its chemical character closely to 

 woody fibre. 



Diastase is a substance obtained from malted barley, and ex- 

 ists in the seeds, and also in oats and wheat. It has the pro- 

 perty of converting starch into sugar, and is used in the pre- 

 paration of dextrine, a substance employed for raising bread. It 

 is supposed to be the peculiar principle of ferments, and hence 

 its great use in culinary operations. 



3. Gums are the exudations of several trees, such as the 

 plum, peach, apple, cherry, etc. but the principal gums are gum 

 arable, from the acacia, vera and arabica, and gum Senegal, from 

 acacia Senegal. 



Lintseed, when macerated in water, is converted into mucil- 

 age, and when this is evaporated to dryness, it leaves a trans- 

 lucent matter behind, similar to gum. The different kinds of 

 gum are classed by Thompson under three vegetable principles, 

 arabin, bassorin and cerassin. Gum arable is principally compo- 

 sed of arabin, and is well known in the shops. Gum Senegal is 

 of similar composition. Mucilage of lintseed is different from 

 the preceding, but one part of it contains arabin. 



Gum Bassora,gum iragacanth and gum kuteera, contain bassorin^ 

 and are articles of commerce. These gums are used by calico 

 printers. The gum from the cherry, apricot, plum, peach and 

 almond tree, contain cerasin, which is the cause of their insolu- 

 bility. Many of the gums are easily soluble, and are used for 

 varnishes. They are also used in medicine to a considerable 

 extent. 



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