Chemical Classification 313 



will boil away, leaving a stronger solution. The 

 element hydrogen is contained in all acids, however, 

 and it is by the replacement of the hydrogen of an acid 

 by a metal that a salt is formed. This replacement 

 may be effected in various ways. 



EXPERIMENT 141. Drop small pieces of magnesium 

 ribbon into a small beaker, one-third filled with hydro- 

 chloric acid. Add more ribbon when that first used 

 is dissolved, and continue the addition till no more 

 action takes place. Evaporate the solution obtained 

 to a small bulk, and allow it to cool. If the evaporation 

 has been sufficient, a mass of small crystals of mag- 

 nesium chloride will form on cooling. 



EXPERIMENT 142. One-third fill a small beaker 

 with dilute nitric acid. Heat this to boiling and drop 

 in small quantities of lead oxide until no more will 

 dissolve. Evaporate and crystals of lead nitrate will 

 be obtained. 



EXPERIMENT 143. Add crystals of washing-soda to 

 some hydrochloric acid until the portion last added 

 refuses to dissolve. Evaporate to a small bulk, allow 

 to crystallise, and taste one of the crystals formed. 



EXPERIMENT 144. Place 20 c.c. of potassium 

 hydroxide solution in a beaker and add a few drops 

 of litmus solution. Fill a burette with diluted sulphuric 

 acid and clamp the burette to a retort stand. Place 

 the beaker containing the alkaline solution under the 

 burette so that the tap of the latter is immediately 

 over the middle of the beaker. Run in the acid, 

 1 c.c. at a time, into the beaker, stirring the liquid in 

 the beaker, after each addition, with a glass rod. 

 When the last portion added causes the colour of the 

 solution to change to red, cease running in the acid, 

 and note the amount which has been added. The 



