342 Miscellaneous Intelligence. 



to me that advantage might, in some cases, be taken of this ac- 

 tion for the removal of colour in glass. The oxide of manganese 

 is added partly to neutralize the green tint which otherwise 

 would, in some cases, he conferred by iron ; but notwithstanding 

 this, some glass to which oxide of manganese has been added, 

 still possesses a green tint. Many specimens of plate glass are 

 thus coloured, though all contain manganese. On exposing such 

 glass to solar light for some time, (from May 7, 1824, to June 

 1825,) whilst parts broken off from the pieces were retained in 

 the dark, it was found that the green tint was very much altered, 

 and the glass considerably ameliorated in colour, an effect which 

 I attribute to the solar light acting upon the manganese ; and 

 even, at this late period, with respect to the glass enabling it to 

 perform the office for which it was at first introduced into the 

 pot.— M. F. 



10, Curious change of colour in Oxides of Cobalt and Zinc. — It has 

 "been observed, that when a mixed solution of zinc and of cobalt 

 is precipitated, so as to furnish a mixture of the oxides, and this 

 mixture be well washed and dried, it forms a white powder, 

 which, when heated in a close vessel, loses water, and becomes 

 of a beautiful green colour, though the oxide of cobalt does not 

 amount to above one-sixth part of the whole. When well prepared 

 it is probable that this compound may be found to be a very useful 

 pigment. 



11. Nature of Colour in Mineral Productions. — A correspondent 

 in the Annals of Philosophy was led to doubt of the constant neces- 

 sity of any specifically colouring ingredient in minerals, from ob- 

 serving that crystallized felspar exhibits a decided red colour, though 

 analysis points out no substance to which it could be owing ; and 

 also from observing that the mineral, after exposure to a strong 

 heat, has the colour entirely destroyed, a colourless glass being- 

 obtained. By accident he obtained an artificial mixture of bo- 

 dies, which exhibited a property of this kind, becoming coloured 

 by particular treatment, though containing nothing to which that 

 colour could be particularly referred. Lime, alumina, silica, soda, 

 and boracic acid, were coarsely mixed together, and exposed to a 

 strong white heat, which produced a semi-vitrified mass of a pure 

 white ; a portion of this was finely ground, and after exposure to 

 a low red heat, not above that of melting silver, was found, 

 with surprise, to have assumed a red colour; which colour, 

 with the increase of heat, entirely disappeared, and the sub- 

 stance assumed, at last, as pure a white as it possessed after the 

 first fusion. A lump of the original mass underwent no change 



