Foreign Literature and Science. 395 



charged with from two to three pounds of powder. The 

 nutnber of seconds which ehipsed between the tiash and 

 the sound, was noted by chronometers furnished hy Bre- 

 guets, one of which denoted even the sixtieth of a second. 



A singular fact in the course of the experiments was, that 

 the tiring wis distinctly heard at Ville-Juif, by all the gen- 

 tlemen, without difficulty, while at the -other station 

 not. one halt the sounds were audible. Very little wind 

 prevailed, and what there was, v»'as in favor of the persons 

 stationed at Montlhery. The reporters do not undertake 

 to tixplain the cause of this difference ; for, say they, we 

 can only offer to the reader, conjectures void of proof. 

 The result of their trials, after all due allowances, is, that 

 at the temperature of 50° F. the velocity of sound is 173.0J 

 toise^, 337.2 metres, 1106.3026 English feet per second. 



36. Steel. — The Society of Encouragement'at Paris, has 

 decreed a gold medal to M. Pradier, who has brought his 

 steel instruments to the highest degree of perfection. He 

 ha? discovered the valuable art of rendering steel very 

 hard, and at the same elastic. His steel blades can be 

 ben!' double, and are yet so hard asto cut iron, without any 

 injury wlsatever to the edge, however tine and thin it may 

 be. This operation was many times repeated by M. Pra- 

 dier, in presence of the committee, and always with suc- 

 cess. 



37. Sal- Ammoniac. — By the accidental combustion of a 

 bed of coal in a mine near St. Etienne in France, in a situ- 

 ation where it could not be extinguished, there is exhaled, 

 in addition to the usual products of the combustion of coal a 

 vapour which becomes condensed on the adjacent substan- 

 ces, in the form of a white salt. It was considered by the 

 country people as salt-petre, and some of the physicians 

 supposed it to be alum. But from experiments made in 

 the laboratory of the school of mines it proved to be very 

 pure sal ammoniac, (hydro-chlorate of ammonia.) During 

 a few dry days the ground becomes covered with an efflo- 

 rescence of this salt, and it continues to increase till dissolv- 

 ed by rain. In the interior of an uninhabited house, are 

 found those fine specimens which now make a shov/ in some 

 cabinets. During the years 1818 and 1819, the production 



