464 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



metrical contraction, the effect of the blows is to give to 

 the bar the aspect of a series of projections, separated by 

 small level spaces. At the time of the collision these spaces 

 are connected, at a certain moment, upon the said face of the 

 bar, by luminous lines passing from one to the other, and 

 presenting altogether an appearance of an X written in lines 

 of fire. The phenomenon is only visible at a certain tem- 

 perature of the bar ; and the bands appear simultaneously, 

 but do not disappear together, so that several of these lumi- 

 nous cross-bars are visible at one time. M. Tresca explains 

 this phenomenon as due to the fact that the band which be- 

 comes luminous is that along which the plastic metal mainly 

 flows at the moment when the change of form takes place 

 under the hammer. The bright streak, therefore, gives an 

 exact knowledge of the mode of distortion that obtains dur- 

 ing the forging. The phenomenon ought to be the same 

 for all metals, except that the relative hardness, capacity 

 for heat, etc., of the metals will determine the brightness, 

 and thence the visibility of the lines. 12 A, X., 401. 



TUNGSTEN-STEEL. 



A simple and, it is claimed, certain process has been per- 

 fected by Biermann, of Hanover, by which a white, exceed- 

 ingly hard and brittle cast iron, containing from five to forty 

 per cent, of tungsten, can be produced, which is adapted to 

 chilled work, and can be added to cast iron in any propor- 

 tions. 15 C, XVII., 1874, 272. 



INCREASING THE HARDNESS AND DURABILITY OF SANDSTONE 

 BY IMPREGNATING IT WITH SILICATE OF ALUMINA. 



Lewin has obtained most excellent results by impregnat- 

 ing the beautiful, pure, and porous sandstone of the quarries 

 of Neuendorf, at Pirna, with silicate of alumina, employing 

 a solution of sulphate of alumina, and one of silicate of pot- 

 ash. The stone thus treated is preferable to marble for 

 many purposes, and is said to surpass decidedly the artificial 

 stone already much used, especially in hardness and appear- 

 ance. By polishing, it can also be made to resemble marble, 

 and by subjecting it to a high temperature it receives a kind 

 of glaze, to which any color may be imparted. In the im- 

 pregnation it can also be colored, according to the use to be 



