198 Miscellanies, 



filings burn with brilliancy, emitting sparks like iron in oxygen. It 

 is imagined that this metal may be useful, and M. Bussy is enga- 

 ged in searching for a cheap and easy mode of reducing it. 



4. Decrepitating Common Salt — Condensation of Gas in it. 

 Dumas. — M. Dumas has examined and described a very curious 

 effect which occurred when some rock-salt, obtained from the mine 

 of Wieliczka, in Poland, and given to him by M. Boue, was put into 

 water. It decrepitated as it dissolved in the water, and gradually 

 evolved a sensible portion of gas. The bubbles of gas were sen- 

 sibly larger when the decrepitations were stronger, and the latter fre- 

 quently made the glass tremble. This salt owes its property of de- 

 crepitating, to a gas which it contains in a strongly compressed state, 

 although no cavities are sensible to the eye. When the experiment 

 was made in perfect darkness no light was disengaged. The gas 

 disengaged is hydrogen slightly carbonated ', when mixed with air it 

 burns by the approach of a light. 



This disengagement of gas will assist in explaining the numerous 

 accidents which have happened from fire-damp in salt-mines. Sev- 

 eral portions of the salt were nebulous, others were transparent. The 

 nebulosities indicated the existence of numerous minute cavities, 

 probably filled with condensed gas, and, in fact a nebulous fragment, 

 dissolved in water, gave more gas than an equal-sized fragment of 

 the transparent salt. 



This new fact, described by M. Dumas, shews how frequent, in 

 the course of geological accidents, are the phenomena to which are 

 due the accumulation of gas in the cavities of mineral substances, and 

 how varied are the substances upon which these phenomena have 

 been exerted. M. Dumas has endeavored to reproduce salt having 

 the power of decrepitating in water like that described. — Revue 

 Encyc. xlvi. 245. 



5. Manufacture of Bicarbonate of Soda. — M. Creuzberg has 

 found a ready mode for the manufacture of this salt, in the circum- 

 stance that the dry alkalies absorb carbonic acid much more quickly 

 than those in solution. Carbonate of soda is therefore deprived of 

 much of its water by efflorescence, and is then subjected to a cur- 

 rent of carbonic acid gas until the bicarbonate is formed ; the time 

 when this takes place is rendered evident by the evolution of heat, 

 and the exhalation of water, which is deposited in drops upon the 

 interior of the vessel. — Bull. Univ. A. xiii. 134. 



