65] Seminormal Caustic Potash Solution 43 



sulphuric acid, as described in the last article, and another with 

 the caustic potash solution just prepared. Run out 10 c.c. of 

 the acid into an 8-oz. beaker. Stand the beaker on a white 

 tile under the KHO burette; add a drop of methyl orange 

 solution (paragraph 59), stir with a glass rod, and run the alkali 

 solution from the burette, drop by drop, into the beaker, stir- 

 ring continually until the colour changes from red to yellow. 

 When the solution is just neutralised one drop of alkali should 

 make the change from red to yellow. Read off the amount of 

 alkali used and repeat the experiment several times. Take 

 the mean of your readings as accurate. 



The next operation is to dilute your solution to seminormal 

 strength. 



Suppose that the amount of alkali which neutralises 10 c.c. 



of ~ H 2 S0 4 is x. 

 2 



Then x c.c. must be diluted to 10 c.c, or ioax c.c. must 

 be diluted to a litre. 



Measure out in a graduated litre cylinder ioojc c.c. of alkali 

 solution. Make up to a litre with distilled water, shake up well 

 and store in a clean well-stoppered Winchester quart bottle. 



The solution should now be seminormal — i.e., it should 



contain 5- grams of KHO per litre. 



2 



A fresh experiment should be made with this seminormal 



solution to see that 10 c.c. of the — sulphuric acid is exactly 



2 



N 

 neutralised by 10 c.c. of the _ alkali. 



65. The two solutions whose preparation has just been 

 described are used very largely in the estimation of nitrogen 

 (see Part III.). Greater accuracy is, however, obtained by 



using a — solution of caustic potash. To prepare this it is 



