454 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



faces, to be afterward wiped off, will preserve their lustre un- 

 changed for a long time. 13 6', May, ix., 495. 



BEST TOWDER FOE, POLISHING GLASS OR METAL. 



According to The London Engineer, the best powder for 

 polishing glass or metals is probably that used by Lord Ross 

 in preparing the mirror of his great telescope. This is pre- 

 pared by extracting the peroxide of iron from a solution of 

 pure sulphate of iron by precipitating it by means of ammo- 

 nia. The deposit is washed, pressed until almost dry, and 

 then brought to a dull red heat, just visible in the dark. The 

 only points of importance are in reference to the purity of 

 the sulphate of iron, the use of ammonia in considerable ex- 

 cess, and the taking care not to allow the heat above that 

 just indicated. The resulting powder should be a pale red, 

 slightly tinged with yellow. 3 B, August 4,608. 



CUTTING GLASS AND STONE BY SAND BLAST. 



At a meeting of the Massachusetts Institute of Technolo- 

 gy, held on March 16th, 1871, an interesting paper was pre- 

 sented by Mr. James Hamblett, upon Tighlman's process for 

 etching upon glass and cutting stone by a blast of sand. For 

 this purpose the glass or stone is simply covered with paper, 

 cut or perforated in the desired pattern, and then exposed to 

 the sand blast, which cuts the material wherever the surface 

 is entirely exposed in a very delicate and well-defined man- 

 ner, the elasticity of the paper apparently preventing the ac- 

 tion of the sand on the covered parts. We have not room 

 for the details of the process by which the sand is directed 

 against the glass, but there seems no doubt that the meth- 

 od promises an important revolution in decorative and con- 

 structive art. In eight seconds a pane of common window- 

 glass can be ground or roughened, while ordinary sunk let- 

 ters in marble, an inch and a half long, can be cut out in less 

 than a minute. 



Attention was called by Dr. Kneeland to the agency of a 

 similar principle in nature, and reference made to the obser- 

 vations of Mr. Blake upon the action of the drifting sand on 

 the granite at San Bernardino Pass, in California. Accord- 

 ing to Professor Wyman, glass windows on Cape Cod some- 

 times have holes worn in them by the drifting sands blown 



