194 



SCIENTIFIC AMUSEMENTS. 



with certain other gases without the aid of any liquid solvent to 

 facilitate the action, and without any heating being requisite to 

 start the chemical change ; usually the 

 products of the combination are solid at 

 the ordinary temperature. 



Prepare two gas generators with the 

 delivery tubes bent downwards. Into 

 one put a tablespoonful of common salt, 

 and pour over it a wineglassful of 

 strong sulphuric acid; the mass will 

 foam up, a choky corrosive acid gas 

 being disengaged, termed hydrochloric 

 acid (Expt. 175) (the solution of hydro- 

 chloric acid used in so many of the 

 preceding experiments is simply a solu- 

 tion of this gas in water, just as solution 

 of ammonia is ammonia gas dissolved 

 in water). Into the other put some 

 "liquor ammonias fort." (strong solution 

 of ammonia), and warm it so as to 

 evolve ammonia gas, in the same way 

 as in Expt. 160. Bring the delivery 

 tubes of both generators into the same 

 bottle or gas jar, and gently heat each 

 generator so as to drive off gas. The two gases meeting together 

 in the central bottle will unite, forming a white solid which will 

 deposit in the bottle and on its sides. This solid is in fact sal- 

 ammoniac, which (as already shown) can be formed by the com- 

 bination of ammonia and hydrochloric acid in solution (Expt. 

 138); the action of lime on salammoniac, as described in Expt. 

 263, is really to reverse this action, and cause the salammoniac to 

 be decomposed into ammonia gas which is evolved, and hydro- 

 chloric acid which is retained, the lime combining with it. 



If a glass rod moistened with strong hydrochloric acid solution 

 be brought near the mouth of a test-tube in which ammonia is 

 being generated (as in Expts. 160 or 203), more or less copious 

 white fumes will be visible, the formation of which serves as a test 

 for ammonia and analogous volatile alkaline vapours when it is 

 desired to know if such bodies are being evolved. Conversely, a 

 rod moistened with strong ammonia will give similar thick smoky 

 fumes if brought near to a vessel from which acid vapours are 

 escaping, such as the mouth of an unstoppered bottle containing 

 strong hydrochloric acid solution. 



Moisten two tumblers or wide-mouthed bottles internally, one 



Fig. 86. Air burning in 

 Coal Gas. 



