82 



SCIENTIFIC AMUSEMENTS. 



Get a stout flask or bottle of white glass ; provide a well-fitting cork 

 to the mouth, perforated with a round hole through which passes, 

 air-tight, a piece of glass tube 10 or 12 inches long, and drawn 

 out at the end inside the bottle, so as to make a moderately 

 fine jet. The flask should be quite dry inside, and then 

 filled with ammonia gas, as in Expt. 75. When it is judged 

 that practically all air has been displaced, the flask is lifted off the 

 delivery pipe and the cork inserted in its mouth ; the cork and 

 tube should fit perfectly air-tight, which is best ensured by using 

 a perforated india-rubber bung, or by means of sealing-wax, or 

 thoroughly greasing with tallow, &c. Place the flask so that 

 it shall be supported by the ring of a retort stand (fig. 6), with 

 the projecting tube dipping some inches into a vessel of cold 

 water, and then pour a little cold water over the flask. This will 

 cause the gas inside to cool a little, and consequently contract 

 (Chapter XIX.) ; the external atmospheric pressure therefore forces 

 a little water up the pipe to the drawn-out jet. As soon as this 

 water comes in contact with the ammonia gas it dissolves some of 

 it, and consequently produces a partial vacuum inside the flask, 



Fig. 45. Ammonia Fountain. 



the result of which is that the atmospheric pressure forces the 

 water up the pipe with some considerable degree of violence, pro- 

 ducing a vigorous miniature fountain (fig. 45). If the flask is 



