ALKALIES 149' 



72. CAUSTIC POTASH. 



When the metal potassium is added to water, an action similar 

 to that with sodium is noticed ; but in this case the metal takes fire 

 and burns with a violet coloured flame. The resulting solution is 

 indistinguishable from caustic soda by its action on other substances, 

 they are so much alike. The white solid obtained on evaporation is 

 called caustic potash or potassium hydroxide. The compounds may be 

 distinguished from one another by the colour which they impart to a 

 Bunsen flame. Potash gives the flame a violet colour which is visible 

 through a piece of blue glass. Soda colours the flame a bright yellow, 

 but the colour disappears when viewed through blue glass. 



73. CALCIUM HYDROXIDE. 



i. Calcium oxide. Take a piece of calcium metal about the size of a 

 large pea, and hold it by means of a piece of stout copper wire rolled round 

 it. Place some clean dry sand in the bottom of a gas jar and fill it with 

 oxygen by displacement of the air. Heat the calcium to redness and 

 quickly plunge it into the gas. It burns brilliantly and destroys the piece 

 of wire rolled round it. When cool, shake up the contents of the jars 

 with distilled water, and filter. 



ii. Effect of calcium hydroxide on substances. Examine the action of 

 the solution obtained in i. on (a) a solution of copper sulphate, (6) a solution 

 of green vitriol, (c) a solution of washing soda, (d) litmus. 



Calcium hydroxide. Calcium is a silver white metal, which tarnishes 

 when exposed in air, but not nearly so quickly as sodium. It bums 

 brilliantly in oxygen, giving out great heat. The calcium oxide formed 

 is a white solid, which gets hot when water is added to it, forming 

 calcium hydroxide. It is slightly soluble in cold water and less soluble 

 in hot. The solution turns litmus blue. It has not a soapy feel, but 

 its action on most substances resembles that of caustic soda. 



74. AMMONIA. 



i. Preparation of ammonia. (a) Place some ammonia solution in a flask 

 and boil, allowing the gas that is evolved to pass over quick-lime or solid 

 caustic potash in order to dry it. Collect several jars of the gas as shown 

 in Fig. 100. Observe the gas has the same smell as the liquid and acts 

 similarly on red litmus. 



ii. Properties of ammonia. (a) In one jar place a lighted taper. 

 (6) Place a second jar in water and note the rapid absorption of the gas 

 and the rise of the water in the jar. 



