102 
The characteristics of thorianite, determined by Professor Wyndham 
Dunstan, are:—Colour—dull-black to dark-brown on weathered surfaces, 
but bright-black where newly fractured. Streak—Brownish, with green 
tinge. Hardness—7. Specific gravity—8 to 9.5. Blowpipe tests— 
Infusible, but decrepitates and gives off bright scintillations. In borax and 
microcosmic salts gives uranium reactions. In reducing flame gives green 
colour. Composition—ThO^ 58 per cent, to 79 per cent., Uranium 
oxide—52 per cent, to 13 per cent. It contains a considerable amount of 
occluded helium. Occurs in Ceylon in river gravels with other minerals 
* of high specific gravity, such as ilmenite, zircon, and spinel. 
Salts prepared from it are used for incandescent mantles. One of the 
best means of testing whether a mineral is thorianite or a pseudomorph 
after pyrites is by its action on a photographic plate. A piece of lead 
or tin an inch square with a hole pierced in the middle is laid on the film 
of the plate, and the hole in the metal is covered with the mineral. This 
operation must be carried out in the dark. Then the plate, &c., must be 
left in a completely dark place for a day or so. If an image of the hole 
is found on developing the plate in a dark room the mineral is probably 
thorianite or some similar radio-active mineral. If in its other charac¬ 
teristics it corresponds to thorianite there can be 1 if tie doubt that it is 
that mineral. 
[Report sent in zd./.cy.] 
