160 SCIENTIFIC AMUSEMENTS. 



the air ; if this be collected in a stout globular flask or bolthead 

 (the collecting bottle being mouth upwards), and if a cork and glass 

 tube be then placed in the mouth of the bottle, and the whole 

 treated as the similar ammonia flask in Expt. 77, the same result 

 will be brought about, viz., the formation of a miniature fountain, 

 because of the pressure of the air forcing water into the flask, 

 owing to the diminution in bulk of the gaseous contents thereof, 

 when water comes in contact with them so as to begin to dissolve 

 them. The liquid resulting is a weak aqueous solution of hydro- 

 chloric acid ; by employing arrangements in which comparatively 

 small quantities only of water are brought in contact with the gas, 

 stronger solutions are obtained ; when the water is nearly saturated 

 with the gas (to produce which result it has to absorb several 

 hundred times its volume of the gas), the liquid fumes more or less 

 in the air. Such solutions of hydrochloric acid are those employed 

 (sometimes after diluting to weaken them somewhat) in various of 

 the experiments above described, such as Nos. 10, 13, 99, 118, 

 fee. 



5. Chemical Actions producing Change of State without 

 the Employment of Solvents. 



CHAPTER XIII. 

 CHEMICAL ACTIONS OP DECOMPOSITION OR BREAKING-UP. 



We have already seen (Chapter I.) that most chemical actions 

 are referable, in the first instance, to one or other of the three 

 classes simple decomposition or breaking-up (e.g., where water is 

 decomposed by electricity into oxygen and hydrogen gases) ; com- 

 bination or synthesis (e.g., where a mixture of oxygen and hydro- 

 gen is fired, so as to cause the two gases to unite together and form 

 steam) ; and reciprocal decomposition, where two substances so 

 react upon each other as to produce two new products, each different 

 from the original materials (e.g., where zinc and hydrochloric acid 

 give hydrogen and chloride of zinc, or where iron sulphide and 

 hydrochloric acid give sulphuretted hydrogen and iron chloride ; 

 these two changes being reactions of single displacement and 

 double displacement respectively). 



