84 



always fairly satisfactory, and agreed very well with the colour given with 

 known weights of manganese salts. The following is the percentage amount of 

 manganese (Mn) contained in the ash of the timber of the several species of Callitris 

 determined as above. The shaxings were taken from o\qy the x\hole surface of 

 the piece of timber, and in no instance was a solid portion of the wood ignited. 



Callitris 



gracilis 



=0-230 per 



cent. Mn. 



') 



intratropica 



=o-ii6 









Macleavana 



=0-073 









Tasmanica 



=0 064 









rhomboidca 



=0-058 









glauca 



=0-058 









arenosa 



=0-019 









verrucosa 



=0-016 









calcarata 



=0-016 









MncUeri 



=0-015 









rohiista 



= 0-010 





To arrive at some conclusion as to the darkening power of a small quantity 

 of oxidised manganese in organic material of this class, the amount of manganese 

 in the precipitated dark gum from Araucaria Cunninghamii was determined, and 

 also that in the still darker precipitated gum from Agathis robusta ; 0-3 gram of 

 the air-dried black gum from Agathis robusta was ignited and the ash boiled with 

 the same amount of nitric acid and lead peroxide as in the previous determinations ; 

 I c.c. of the standard potassium permanganate then required to be diluted to 

 25 c.c. to match the colour given by the ash of the gum ; the amount of manganese 

 in the air-dried black gum of Agathis robusta was, therefore, 0-0046 per cent. 



With the dark gum of Araucaria Cunninghamii the same process was 

 followed, 0-3 gram of the air-dried gum being taken. The standard perman- 

 ganate then required to be diluted thirty times to obtain the correct tint, so that 

 this black gum contained 0-0038 per cent, of manganese. It is thus seen how 

 small an amount of manganese is required to render the gum precipitate almost 

 black and opaque. 



The amount of manganese in the ash of the timber of Aga'his robusta was 

 0-145 per cent., and in only one instance was this amount exceeded with the 

 Callitris. The ash of the timber of Araucaria Cunninghamii contained 0-054 P^r 

 cent, manganese, while that of the timber of Araucaria Bidwilli contained 0-077 P^^" 

 cent, manganese. 



With trees belonging to other genera, the ash of the timber of A ctinostrobus 

 Pyramidalis contained 0-077 pcr cent, manganese, and tliat of Podocarpus data 

 0-0024 per cent. With regard to the latter tree it is interesting to notice that the 

 cells containing the dark material, as shown under the microscope, were considerably 

 less in quantity in this timber than in that of any of the species previously 

 mentioned; so that this tree evidently uses manganese in smaller amount than 

 that generally required by its congeners. 



