NEUTRAL SUBSTANCES. 123 



dens into a brittle solid, of a transparent, reddish-brown color, 

 and of a bitter and aromatic taste. It was known and used by 

 the ancients. In medicine, it is considered as a tonic. The 

 alcoholic tincture is used as a wash for the teeth. 



Olihanum is the frankincense of the ancients. According to 

 Lamark, the Arabian variety is obtained from the amysis gilead- 

 cn5i5,. while Mr. Colebrook derives the Indian olibanum from a 

 large tree growing on the mountains of India, boswella serrata. 

 It is a brittle, white-yellow substance, of an acrid and aromatic 

 taste, and, when burnt, diffuses an agreeable odor, on which 

 account it is much used as a perfume. 



Opium is a sedative gum-resin, which exudes from the heads 

 of the papaver somniferum, or poppy, great quantities of which 

 are used in medicine. It is also taken in large quantities as a 

 stimulant, in which case it is highly poisonous. 



Class IV. Neutral Substances are those vegetable principles 

 which possess, neither the properties of acids nor bases, and 

 which, so far as is known, do not combine in definite propodions* 

 with other substances. Under this class are arranged a very 

 great number of useful substances. Those that are of particu- 

 lar interest to the agriculturist, may be included under the 

 following heads : sugars, amylaceous substances, gums, gluteiwus 

 svhstances, caoutchouc, extractive, and bitter principles. 



I. Sugar (Ci2HioOio=]62) is a term applied to substances 

 characterized by their sweet taste. It is found generally in 

 the juices of plants, from which it is extracted by boil- 

 ing or evaporation. The sap of common sugar is obtained from 

 the sugar-cane (arundo saccharifera), the sugar-maple [acer sac- 

 charinum), and from the beet-root. This latter source of sugar, 

 was introduced into France by Bonaparte, during the war be- 

 tween France and England, and in the year 1 827, the quantity 

 manufactured was 2,650,000 lbs. The modes of making sugar, 

 derived from these sources, are various, and can only be alluded 



* Most bodies, as the acids and alkalies, combine with other bodies 

 in definite proportions ; that is, definite quantities of one body combine 

 with definite quantities of another body, to form a third body. See 

 Introduction. But there are also a large class of bodies, both organic 

 and inorganic, which do not observe this law, and are said to unite in 

 indefinite proportions. Water and sulphuric acid, for example, will 

 unite in all proportions. Most substances which are held in solution 

 in water, unite with it in indefinite proportions, up to the point of satu- 

 ration; such as salts, sugars, gums, etc. 



