100 



form and appearance in all species, being well denned monoclinic crystals, in stout 

 microscopic prisms, averaging 0-0174 mm. in length and 0-0077 mm. in breadth, and 

 containing one molecule of water. A peculiarity of these is the tendency to form twins 

 geniculate in appearance ; twinned forms being pronounced in some species. The 

 theory is advanced that some of the " Mallees " or shrubby Eucalypts have been formed 

 through the poisoning effect of the excess of this substance, acting for a long time upon 

 species which originally grew as large trees. The tannins in those Eucalyptus barks 

 containing a large amount of calcium oxalate are of very good quality, light in colour, 

 astringent, easily soluble, and should make leather of good quality. On evaporating 

 the extract to dryness on the water-bath, but little darkening takes place, and the 

 product is still readily soluble. 



He goes on to say that this class of Eucalyptus barks should, therefore, make 

 excellent tanning extracts. From the bark residue the calcium .oxalate should be 

 profitably extracted, and the oxalic acid obtained cheaply from this, practically as a 

 by-product. The air-dried bark of Eucalyptus salubris, the " Gimlet " of West Australia 

 gives 30-5 per cent, of total extract and 18-6 per cent, of tannin absorbed by hide powder 

 and contains 16 per cent, of calcium oxalate. The bark of E. gracilis contains 16-66 

 per cent, of calcium oxalate; that of E. Behriana, 16-5 per cent.; of E. oleosa, 10-64 

 per cent. ; of E. dumosa, 9-8 per cent. ; and of E. salmonophloia, 8-34 per cent. The 

 barks of all the Eucalypts tested contained calcium oxalate, although in some species 

 in very small amount. 



" The Mallees which contain the crystals in greatest abundance seem to be those 

 species which have a very thin, smooth bark." 



" E. salmonophloia and E. oleosa, being apparently the same tree in different 

 forms of growth, it is probable that the latter is a stage in the slow, and permanent 

 degeneration of the larger tree " (p. 26). 



' The form of calcium oxalate peculiar to Eucalyptus barks contains one molecule 

 of water, and has the composition and crystalline form of the mineral Whewellite, with 

 which substance it is perhaps identical." (p. 26.) 



Mr. Smith found percentages of calcium oxalate in the following barks : — 



E. gracilis, 16-66. E. occidentalis, 6-82. 



E. Behriana, 16-50. E. viridis (acacioides), 5-01. 



E. salubris, 16-00. E. redunca, 4-46. 



E. oleosa, 10-64. E. fruticetorum (polybractea), 2-14. 



E. dumosa, 9-80. E. stricta, 0-69. 



E. salmonophloia, 8-34. E. Morrisi, 0-08. 

 The substance occurs also in E. pumila. 



