158 Intelligence and Miscellaneous Articles. 



The following are some results which I have obtained by opera- 

 ting with plates cut out of one and the same cobalt glass. At the 

 temperature of fusion of platinum, two of these plates superposed 

 were sufficient to give sensibly the purple tint : this I have been 

 able to observe leisurely at the Conservatoire des Arts et Metiers 

 at the time of the fusion of the platinum for making the interna- 

 tional metres, at which operation I had the good fortune to be 

 present. Shortly after, thanks to your kindness, I had the oppor- 

 tunity of attending in your laboratory at the experiment of the 

 fusion of iridium : at the instant of the maximum of temperature, 

 this source of light, viewed through the same two plates, appeared 

 perfectly blue ; but with three plates the tint was purple, of a shade 

 exactly like that given by a gas-flame seen through two plates. 

 Now, if the sun is observed high above the horizon in a clear sky, 

 the purple tint is not obtained with three, or four, or even with 

 six plates superposed. A great thickness of cobalt glass is requi- 

 site in order to get this shade on the edge of the sun's disk ; and 

 part of the effect is doubtless to be attributed to defects of homo- 

 geneity in the glass which I employed. The light of the moon 

 gives the same result, showing that the intensity has no influ- 

 ence. — Bibliotheque Universelle, Archives des Sciences, Feb. 1875, 



ON FUSED BORACIC ACID AND ITS TEMPERING. 

 BY V. DE LTJYNES. 



Fused boracic acid, which closely resembles glass in external 

 characters, presents the following remarkable properties. 



In the viscous state it can be drawn out in threads which rapidly 

 solidify ; and in this respect its ductility resembles more that of 

 silica than that of glass properly so called. 



Its hardness, between 4 and 5, places it between fluorine and 

 apatite ; it scratches glass ; it is found to be with difficulty cut by 

 means of sand, grit, or emery either dry or with oil : to grind it 

 the solvent action of water must be interposed ; and in this case the 

 cutting takes 7 or 8 times as long as that of common glass in the 

 same circumstances. This resistance to grinding, which does not 

 correspond to its hardness, is doubtless due (as M. Damour has as- 

 certained in the case of other minerals) to a peculiarity of structure. 



Fused boracic acid in mass is slowly hydrated in contact with 

 water ; but when pulverized the action is rapid, as Ebelmen has 

 shown. When powdered boracic acid is moistened with water, it 

 increases in volume, and the temperature of the mixture rises to 

 nearly 100°. 



Boracic acid is remarkable especially for the energy and persist- 

 ence of its tempering. By running it upon a cold metallic surface 

 vitreous plates are obtained, of which the lower surface, cooled by 

 the metal, is more strongly tempered, and consequently more di- 

 lated than the upper surface. Hence results a flexure which may 

 be sufficiently great to determine the rupture of the plate and its 



