452 COMPOUND PRODUCTS. CHAP. I. 



layer, which is cork, is then stripped off, and to 

 flatten and reduce it to sheets, it is put into water 

 and loaded with weights. The tree continues to 

 thrive, though it is thus stripped of its cork once in 

 two or three years, 



Cork is a light, soft, and elastic substance, dis- 

 tinguished by the following properties. Its colour 

 is a sort of light tan. It is very inflammable and 

 burns with a bright white flame, leaving a black and 

 Properties, bulky charcoal behind. When distilled it yields a 

 small quantity of ammonia. Nitric acid corrodes 

 and dissolves it, changing its colour to yellow, and 

 finally decomposes it, converting it partly into an 

 acid, and partly into a soft substance resembling 

 wax or resin. The acid which is thus formed is 

 denominated the Suberic acid, and has been proved 

 by the experiments of Lagrange to be an acid of a 

 peculiar nature.* 



It seems probable that cork exists in the bark of 

 some other trees also as well as the Quercus Suber. 

 There is a variety of the Ulmus campestris, com- 

 mon in hedge-rows, whose bark assumes something 

 of the external appearance of cork, which it resem- 

 bles in its thickness, softness, and elasticity, and in 

 its loose and porous texture, as well as also in its 

 chemical properties. -j~ Fourcroy seems, indeed, to 

 regard the epidermis of all trees whatever to be a 

 sort of cork, but does not say on what grounds his 

 opinion is founded. 



"* Connais. Chim. vol. viii. p. 98. f Ibid. 



