PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 627 



which they succumb to the attacks of marine animals, the Teredo 

 and the Chelura. The Swan River Mahogany, a species of Euca- 

 lyptus, is the only wood yet used there which entirely resists these 

 agencies. There are no pines in Australia. Pine for inside work 

 of houses is mostly imported from America. 



Australian Barks. 

 The barks of many varieties of trees are remarkable for their 

 astringent qualities, and contain a large percentage of tannin. 

 Those used in the manufacture of leather are from various Wattle 

 trees belonging to the Acacia family. They impart to the leather 

 a reddish brown color, darker than American oak-tanned, and 

 more nearly resemblmg that produced by the American hemlock. 



AuSarRALIAN EsSENTIiVL OiLS. 



J. W. Osborne, Esq., formerly of Australia, states that leaves 

 from which essential oils can be extracted, constitute the great 

 bulk of the forest vegetation. The yield of Dandenong (Eucalyp- 

 tus Amygdalina) is astonishingly plentiful — 130 pounds of freshly 

 gathered leaves, including small branchlets, to which they are 

 attached, give upward of three pints. The oil exists ready formed 

 in the leaf, and the cells containing it may be seen in great num- 

 bers on examination by transmitted light. The oil is a thin, trans- 

 parent fluid, of pale yellow color, having a pungent odor, resem- 

 bling that of oil of lemons, but coarser and stronger ; its taste is 

 rather mild and cooling, producing an after sensation in the mouth, 

 resembling camphor, with something of its bitterness. Its specific 

 gi-avity at 60° F. is 0.881. The boiling point is 330. It is some- 

 what less volatile than turpentine. Like other essential oils, it 

 leaves no stain on paper, and in shallow vessels it absorbs oxygen, 

 giving rise to a residual resinous matter. When brought in con- 

 tact with iodine, no explosion ensues, even when the temperature 

 is raised, but a dark colored solution is created, which, wdien 

 heated, emits a peculiarly variegated vapor, in which the colors, 

 yellow, red, violet, green and blue are beautifully visible, particu- 

 larly in sunlight. 



This oil is soluble in all proportions in turpentine., both fat and 

 drying oil, benzine, naptha, ether, chloroform and absolute alco- 

 hol. Its power for dissolving resinous substances may be esti- 

 mated by the following : In one pint of the oil aj-e solable 23.3 

 av. ounces of camphor, or 20.3 ounces of rosin, or 17.5 of mastic, 



