CH. I.] 



STANDARD SODA. 



25 



Sodium Hydroxide. 



Dissolve 100 grams of the best NaOH in 100 cc. of distilled 

 water in an Erlenmeyer flask of resistance glass. Cover the mouth 

 of the flask with tin foil, and allow the 

 solution to stand over-night till the carbon- 

 ate has mostly settled. Cut a hardened 

 filter paper to fit a Buchner funnel. Treat 

 it with warm strong [i : i] NaOH solution. 

 Decant the soda and wash the paper first 

 with absolute alcohol, then with dilute 

 alcohol, and finally with large quantities 

 of distilled water. Place the paper on the 

 Buchner funnel and apply gentle suction 

 until the greater part of the water has 

 evaporated. Now pour the concentrated 

 alkali upon the middle of the paper, spread 

 it with a glass rod, and filter under suction. 

 The clear solution is now diluted quickly 

 with cold distilled water, that has been 

 recently boiled to remove C0 2 , to make 

 approximately N. NaOH ; 10 cc. of this 

 is withdrawn and roughly standardised 

 against N. HC1. It is then diluted till it is 

 approximately 0-2 N with CO 2 -free water 

 and the solution poured into a paraffined 

 bottle, to which a burette and soda-lime 

 guard tubes have been attached (see fig. 6). 

 The solution is then accurately standardised against weighed amounts 

 of the pure acid potassium phthalate. To do this accurately weigh up 

 about 1-5 gms. of the salt, dissolve in about 30 cc. of distilled water, 

 add phenol phthalein and titrate with the alkali till a faint but dis- 

 tinct and permanent pink is developed. A current of CO 2 -free air 

 should be blown through the solution during the titration. The 

 apparatus shewn in fig. 35 is convenient for this purpose. 



If p be the exact weight of the phthalate taken, and s the 

 volume of soda required, the normality of the soda is 



T-OOO x p 



Fig. 6. Paraffined bottle 

 (A) for storing standard 

 alkali. B and C are 

 soda lime tubes. The 

 burette is filled by 

 sucking at C. 



= a. 



204-14 x s 



