Intelligence and Miscellaneous Articles. 397 



so that if the material of the cone were perfectly uniform, the dykes 

 produced would be wedge-shaped. But, from the absence of this 

 uniformity and other causes, fissures commenced at the interior and 

 propagated into the mass of volcanic cones can rarely be uniformly 

 distributed round the crater or produced in regular vertical planes 

 in a truly radial direction. Hence the author concluded that it is 

 unsafe to attempt to fix the position of an ancient crater by means 

 of the intersection or concurrence of the lines of apparent orientation 

 of dykes alone. The author stated that the intrusion of volcanic 

 dykes cannot so greatly influence the slope of volcanic mountains 

 as has been supposed. 



XLIX. Intelligence and Miscellaneous Articles. 



ON THE REACTIONS OF METALLIC THALLIUM BEFORE THE BLOW- 

 PIPE. BY E. J. CHAPMAN,, PH.D.,, PROFESSOR IN UNIVERSITY 

 COLLEGE, TORONTO*. 



HPHE following reactions are given from direct experiments by 

 the writer t. 



In the closed tube thallium melts easily, and a brownish-red 

 vitreous slag, which becomes pale yellow on cooling, forms around 

 the fused globule. 



In the open tube fusion also takes place on the first application 

 of the flame, whilst the glass becomes strongly attacked by the for- 

 mation of a vitreous slag, as in the closed tube. Only a small 

 amount of sublimate is produced. This is of a greyish white colour ; 

 but under the magnif ying-glass it shows in places a faint iridescence. 



On charcoal, per se, thallium melts very easily, and volatilizes in 

 dense fumes of a white colour streaked with brown, whilst it im- 

 parts at the same time a vivid emerald-green coloration to the 

 point and edge of the flame. If the heat be discontinued, the 

 fused globule continues to give off copious fumes ; but this action 

 ceases at once if the globule be removed from the charcoal. A de- 

 posit, partly white and partly dark brown, of oxide and teroxide is 

 formed on the support ; but, compared with the copious fumes 

 evolved from the metal, this deposit is by no means abundant, as 

 it volatilizes at once where it comes into contact with the glowing 



* Commimicated by the Author. 



t The reactions given by Crookes are as follows : — "The metal melts 

 instantly on charcoal and evolves copious brown fumes. If the bead is 

 heated to redness it glows for some time after the source of heat is removed, 

 continually evolving vapours which appear to be a mixture of metal and 

 oxide. A reddish amorphous sublimate of protoperoxide surrounds the 

 fused globule. AYhen thallium is heated in an open glass tube it melts 

 and becomes rapidly converted into the more fusible protoxide, which 

 strongly attacks the glass. This oxide is of a dark red colour when hot, 

 solidifying to a brown crystalline mass. The fused oxide attacks glass 

 and porcelain, removing the silica. Anhydrous peroxide of thallium is a 

 brown powder, fusing with difficulty and evolving oxygen at a red heat, 

 becoming reduced to the protoxide. The phosphate and sulphate will 

 stand a red heat without change." 



