SCIENTIFIC NEWS. 229 



Mr. Pietet accordingly recommends to those who are en- 

 gaged in mining a combination of the two methods ; one of 

 which, the blasting with sand, would give security to the 

 miners; the other, a partial vacuity, would save powder. His method. 

 This may easily be effected, by introducing into the hole, after 

 the powder, a cylinder or cartridge of paper, open at one 

 end, and with a small hole in the other, which is to be placed 

 uppermost, to admit the priming straw. Over this the sand 

 may be poured in, and thus a vacuum of two or three 

 inches between it and the powder preserved. 



Mr. Gillet-Laumont suggests another additional contriv- Gillct-Lau- 

 ance. He thinks, if the hole be vertical, or not much in- provement . 

 clined from this direction, a more forcible concussion might 

 be given to the rock, by loading the sand with a heavy 

 weight. To effect this he would introduce into the hole an A heavy weight 

 iron cylinder, with a lateral groove for the passage of the 

 straw, and surmounted by a heavy mass of iron, being a 

 continuation of the cylinder. This he supposes would add 

 greatly to the resistance; and the same piece of iron would 

 serve repeatedly for the same purpose, as it could not be 

 blown far, and therefore would easily be found. 



Extract of a Letter from Mr. Gehlen to J. C. Delame- 



THERIE.* 

 SIR, 



YOU are acquainted with the observations of Sir James 

 Hall on the effects of heat modified by compression +; but 

 Mr. Bucholz has just written to me, that powdered chalk 

 may be converted into a substance analogous to marble 

 without compression. 



Wanting to prepare some quicklime, he put four pounds Chalk fused 

 and a half of pure washed chalk into a Hessian crucible, ^ ac °d. ° bBg 

 which he covered with a brick, and exposed it in a wind 

 furnace for an hour to a bright red heat, not gradually 

 raised. On examining the contents of the crucible, Mr. 



* Journal de Physique, Vol. LXIII. p. 238, Sept. 1806. 

 f See Journal, Vol. IX. p. 98; XIII. p. 328, 381; and XIV. 

 p. 13, 113, 196, 302, 314. 



2 Bucholz 



