acids. 339 



Air, Black. — This gas exists in great abundance in nature, and is 

 often extricated very largely in a variety of chemical operations. 

 It occurs in considerable quantities in marshy places, rises from 

 certain acidulous waters, and abounds in many caverns, par- 

 ticularly in the celebrated grotto Del Cane, near Naples. It is a 

 very frequent cause of accidents in coal-mines, where it is known 

 under the name of choke - damp , in breweries, in places where 

 charcoal is burned in close rooms, and in wells, and other places 

 that have been long shut up. In consequence of its wieght, its 

 specific gravity being 1*5230, it remains at the bottom of those 

 places, and proves fatal to those who incautiously enter, by causing 

 suffocation. The bodies of persons suffocated in carbonic acid gas, 

 exhibit the ordinary appearances of apoplexy. The most effec- 

 tual means of recovering the vital actions, when suspended by this 

 gas, consists in inflating the lungs as soon as the body is removed to 

 the open air, in sprinkling the face, and, when the heat is above 

 the standard of health, even the whole body, with cold water. 

 In other respects the method of treatment will be the same as in 

 the case of drowning or other kinds of suffocation. Those who 

 wish for further information on the subject of this and other nox- 

 ious gases, may consult the valuable "Treatise on Poisons," by 

 Professor Christison. 



Sp. 2. Muriatic, or Hydro-chloric Acib. — In its pure 

 form Muriatic Acid always exists as a gas, and in this form it is 

 said to emanate from volcanoes. It is the only known compound 

 of chlorine with hydrogen, and is, therefore, very properly termed 

 by the French chemists hydro-chlor'me gas. It is best obtained by 

 the action of concentrated sulphuric aeid upon an equal weight of 

 sea salt ; it is given off in great purity, but must be collected over 

 mercury. It has a strong affinity for oxygen, which, according to 

 Sir H. Davy, at the temperature of 40, can absord 480 times its 

 volume of muriatic acid gas. The solution thus formed is com- 

 monly known by the name of muriatic acid, or spirit of salt. It 

 may be prepared by passing the gas, procured as above, imme- 

 diately through water ; or by adding a sufficient quantity of water 

 to the sulphuric acid in the first instance, and then distilling. The 

 solution, when pure, is perfectly colourless, and possesses all the 



