Intelligence and Miscellaneous Articles. 79 



there is formed at the expense of the lamelliform crystals a silicate 

 disseminated in droplets in the fused salt. This destruction of the 

 tridymite is only temporary, if the silicate be maintained in the 

 liquid bath formed by the acid tungstate, at a temperature between 

 900° and 1000° ; for this silicate then undergoes a decomposition 

 which regenerates the tridymite. This sort of precipitation in the 

 dry way demauds much more time than the crystallization of amor- 

 phous silica. This is why it is more advantageous to heat silica 

 with tungstate of sodium than to decompose an alkaline silicate by 

 tungstic acid. 



The destruction of tridymite, and subsequent precipitation of 

 silica in the form of lamella?, permit the part played by the tungstate 

 of sodium in the act of crystallization to be analyzed. The alkali 

 of the tungstate attacks the silica, producing an alkaline silicate ; 

 and the tungstic acid retakes at a lower temperature the alkali 

 which the silica had taken from it. These two reciprocally inverse 

 actions take place successively when the temperature oscillates be- 

 tween certain limits. They suffice to explain the crystallization, 

 without it being necessary to involve the solubility of silica in the 

 fused salt; for these reactions are perfectly comparable with those 

 which determine the crystallization of the sesquioxide of iron when 

 it is heated in gaseous hydrochloric acid. 



Although I cannot at present compare the results furnished by 

 the method I have just made known Avith those which can be ob- 

 tained by a judicious application of M. Gr. Rose's method, I will 

 notice this fact, that the preparation of tridymite by means of tung- 

 state of sodium does not require a temperature so elevated as that 

 which is necessary when acid phosphate of sodium is employed. 

 The phosphoric salt and the tungstate of sodium are both minerali- 

 zers of silica ; but the latter salt exerts a more energetic action than 

 the former, even at a less-elevated temperature — winch permits it 

 to be employed for reproducing the numerous more or less fusible 

 silicates which are associated with silica in the rocks. — Comptes 

 Renclus de V Academic des Sciences, May 6, 1878, tome lxxxvi. 

 pp. 1133-1135. 



OUTLINES OF THE ACTINIC THEORY OF HEAT. 

 BY PROF. C. PUSCHL. 

 In the present form of the mechanical theory of heat, and spe- 

 cially in the kinetic theory of gases, the sum of the vires viva of 

 the ponderable atoms of a body in motion among themselves is re- 

 garded as the quantity of heat of the body ; while the sum of the 

 vires vivce of the aether contained in the body is neglected, and it is 

 assumed that this medium exerts no sensible influence on the 

 motions of the atoms. This presentation the author holds to be 

 inadequate. It is remarked that a hot body may be cooled not 

 merely by contact with colder bodies, but also by radiation, and 

 that the velocity of such a cooling is not always inconsiderable, but 

 under favourable circumstances is so great that many physicists 



