90 FOREST CULTURE AND 



At last, with mild heat and final constant stirring, 

 the whole is evaporated to dryness. This dry mass 

 represents crude potash more or less impure, accord- 

 ing to the nature of the wood employed. 



A final heating in rough furnaces is needed, to ex- 

 pel sulphur combinations, water, and empyreumatic 

 substances; also, to decompose coloring principles. 

 Thus pearlash is obtained. 



Pure carbonate of potassa in crude potash varies 

 from forty to eighty per cent. Experiments, as far 

 as they were instituted in my laboratory, have given 

 the following approximate result with respect to the 

 contents of potash in some of our most common trees. 

 The wood of our She-oaks (Casuarina suberosa and 

 Casuarina quadrivalvis), as well as that of the Black 

 or Silver Wattle (Acacia decurrens), is somewhat rich- 

 er than wood of the British Oak, but far richer than 

 the ordinary Pine woods. 



The stems of the Victorian Blue Gum-tree (Euca- 

 lyptus globulus), and the so-called swamp Tea -tree 

 (Melaleuca erieifolia), yield about a? much Potash as 

 European Beech. 



The foliage of the Blue Gum-tree proved particu- 

 larly rich in this alkali ; and as it is heavy and easily 

 collected at the saw-mills, it might be turned there to 

 auxiliary profitable account, and, indeed, in many 

 other spots of the ranges. 



A ton of the fresh leaves and branches yielded, in 

 two analyses, four and three quarters pounds of pure 

 potash, equal to about double the quantity of the av- 

 erage kinds of pearlash. The three species of Euca- 

 lypts spontaneously occurring close around Melbourne 

 — the Bed Gum-tree (Eucalyptus rostrata) ; the Man- 



