XMI ACIDS, BASES, AND SALTS :io:< 



Fill a burette with the caustic soda solution, and place 25 c.c. 

 of the sulphuric acid solution in a flask. This is done by care- 

 fully sucking up the acid into & pipette until the liquid passes 

 the 25 c.c. mark, then speedily closing the top of the pipette 

 with the finger, and allowing, by slight motion of the finger, the 

 liquid to run out until it is exactly at the mark. To this acid 

 add a drop of litmus, whereby the solution is coloured a bright 

 red. Now run in the caustic soda solution from the burette 

 until the acid is exactly neutralised, the point of neutralisation 

 being known by the change of colour from red to blue, which 

 occurs when the smallest excess of the caustic soda is added. 

 Note carefully the number of cubic centimetres of caustic soda 

 solution required to neutralise the acid. Do the experiment a 

 second time to verify your result, and then perform a similar 

 pair of experiments with the other two acids, and with the 

 caustic potash and the three acids. Your results may be entered 

 thus : 



25 c.c. of 



c.c. of caustic soda 

 required. 



c.c. of caustic potash 

 required. 



Sulphuric acid 15*4 17'3 



Nitric acid 182 20'4 



Hydrochloric acid ... 20 '0 22 -4 



As, however, the strength of the solutions of caustic soda and 

 caustic potash are known, we may instead of the number of c.c. 

 of solution write the number of grams of the dissolved com- 

 pound. Thus suppose that 40 grams of caustic soda and 50 

 grams of caustic potash were used, then 1 c.c. of the solution 

 contains respectively '04 and '05 grams, as that the above table 

 becomes 



