336 LEGUMINOS^ PRODUCING TANNING MATTERS AND DYES 



the figures for tlie same species may vary within fairly wide 

 limits. 



riiis is no doubt the result of vegetative and climatic 

 conditions, which may be more favourable in one locality 

 ihan in another : the age of the plant is also an important 

 factor in this variation; similarly the season in which the 

 crop is taken. 



In the case of the fruit the degree of maturity will cause 

 the proportion of tannin to vary. 



It is not always the same parts of the different plants 

 that give the highest percentages. In some it is the leaves, 

 in others the bark, and in others again the wood. Analysis 

 is thus indispensable in order that the planter may determine 

 what to do with the various trees. 



The sappy bark from the oldest trees should be removed 

 first, and young pods will yield more tannin than those 

 which are nearly ripe. 



The nature of the tannin from the bark and from the 

 pods of the same tree ma}- vary, and similarlv the tannins 

 contained in all Leguminos^e may not be equally efficacious. 

 This no doubt tends to show that their compositions and 

 combinations are not identical, and would explain the short- 

 comings of certain tans. 



The best plan will be to make practical trials in order 

 to determine a choice of species. This is all the more 

 evident when it is seen that the barks of certain plants of 

 the same family give negative results in one country and 

 markedly good results in another. 



According to " Watt's Dictionary of Economic Products," 

 the tannin from the pods of Acacia arabica consists chiefly 

 of gallotannic acid combined with saccharose and other inert 

 substances, whilst that derived from the bark is of a different 

 nature. 



In some countries trees are exploited which have never 

 been cultivated and which are found either in forests or 

 among vegetation which has invaded large tracts of land. 



