44 PROPERTIES OF WOOD. 



wood and brown oak) are naturally of a fine colour ; also 

 desirable colours depend chiefly on fashion, while by bleach- 

 ing, and by the use of acids and dyes, any fashionable colour 

 can be produced. The natural colours of our woods are 

 utilized chiefly in wood-mosaic work. Freshly felled wood, 

 as a rule, possesses a distinct colour, which is only 

 transitory. 



It is by chemical changes only that the surfaces of planks 

 and scantlings, at first exhibiting very little trace of colour, 

 often rapidly acquire a decided tint, e.g., black alderwood ; 

 such tints moreover cannot be fixed and are usually of no 

 economic value. It has been surmised that these changes of 

 colour are due to tannin acted on by oxygen, by the air and by 

 sunlight. Colourless saps and chromogen, that are the bases 

 of madder, indigo and litmus and become coloured by oxida- 

 tion or decay, are absent from wood ; some woods, such as red- 

 wood or pernambuko-wood* (Caesalpinla brasiliensis), contain 

 an extractible dye. Caesalpinia Sappan, cultivated in Southern 

 India and Bengal, said by Gamble to be wild in the Shan 

 States, yields a red dye, that is much used. Logwood (Haema- 

 toxylon campechianum) from the West Indies and Central 

 America, red sanders (Pterocarpus santalinus) from Madras, 

 and other tropical woods, also yield important dyes. All our 

 own woods when boiled yield a brown colouring matter (colour 

 of brown paper). 



Owing to the action of the oxygen of the air, all wood 

 colours become gradually darker ; even what is described as 

 colourless sapwood becomes darker. 



In opposition to the prevailing opinion, we class all woods 

 into two groups from the fact that all species of wood possess 

 a heartwood, whether the latter be externally discernible, 

 owing to its being permeated by colouring matter, or not. 

 In both these cases, the heartwood has physiological func- 

 tions, which the sapwood cannot fulfil permanently (water 

 transport). It is better to renounce such terms as sapwood 



* [Mathey, op. cit., p. 7, terms this Brazil-wood, but states that it comes from 

 Caesalpinia crista and C. e.cliinata of Guiana. Stone (" Timbers of Commerce ") 

 gives Chlorophora tinctor'm, from Cuba and Brazil, as the origin of Fustic 

 {Gellx's BrazUkolz). Mathey mentions Jlijpcrn-utn Ixiccifi'riun (yellow) and 

 (\>i>a'ift>ni bracteata (violet), (Juiana.- Tr. 



