134 SCORODITE IX RHODESIA. 



is greenish-grey, and Avhen crystalline it has a pretty greenish- 

 grey to pale-green, semitransparent vitreous to adamantine and 

 resinous lustred appearance. The crystals are all very small 

 and in aggregates, :but many of them sliow good faces. The 

 compact, close-grained variety often has a marbled appearance 

 suggestive of serpentine. In some specimens grains and crystals 

 of mispickel mav be observed to be altering marginally to scoro- 

 dite. 



Alteration. — As may be gathered from the above remarks, 

 scorodite is observed to alter to limonite and possibly also to 

 arsenolite — arsenic trioxide (As.^O.,) — but this latter mineral 

 needs to be carefully tested for, and the author was not able 

 to detect it. 



Composition. — A quantitative chemical analysis tof the 

 mineral from Gwanda made by 'Sir. J. B. Bull gave: — 



Arsenic pentoxide SO-53 per cent. 



Ferric oxide . . . . .3349 



A\'ater (combined) ^5-98 ,, 



lOO.OO 



The material used for analysis was a mixed sample of amor- 

 phous and finally crystallised green scorodite. A little quartz 

 was observed to be present. 



Economics- — ^The mineral was iirst brought to my notice 

 whilst Curator of the Rhodesia Museum on account Of con- 

 siderable bodies of it having been pegged for gold. Free gold 

 is associated with the mineral at Gwanda and apparently else- 

 Avhere, but since the mineral appears to be only a surface cap- 

 ping, it is not likely of itself to be important as a gold ore. 

 At a small depth the gossan gives place to lodes of arsenical 

 pyrites from which the gold is less easily extracted ; interest in 

 it as a gold ore has somewhat decreased therefore. Still the 

 mineral has 'considerable importance. as an indicator of arsenical 

 pyrites which commionly contain gold and silver in amounts 

 which mav be profitably extracted. 



Soya Bean Rubber.— The manufacture of a syn- 

 thetic substitute for indiarubber has recently been patented in 

 Germany. The basis of this preparation is the oil of the Soya 

 Bean which is subjected to the following treatment. Nitric acid 

 is allowed to act upon the oil in such a manner as to reduce it to 

 the consistency of a thick paste. This paste is repeatedly washed 

 with an alkaline solution, after which it is heated to a tempera- 

 ture of 150 degrees Centigrade. A homogeneous substance is 

 thus obtained which possesses the property of elasticity, and, in 

 addition to resembling true indiarubber in other ways, is declared 

 to be capable of vulcanisation. 



