66 TESTING MISCELLANEOUS SUPPLIES. 



obtainable. Devine's method a avoids this danger. For this method three stand- 

 ard solutions are used : 



1. Tenth-normal hydrochloric acid. 



2. Tenth-normal caustic soda or potash in alcohol. 



3. Tenth-normal stearic acid in alcohol. 



Solution No. 1 is used to standardize No. 2; Nos. 2 and 3 should be titrated 

 against one another warm, using phenolphthalein as indicator. 



Weigh 2 grams of soap (which needs no drying) into a round-bottomed flask 

 of about 300 cc capacity, and pour 50 cc of alcohol upon it. Run in sufficient 

 tenth-normal stearic acid from a burette to neutralize the free alkali in 2 grams 

 of the soap, add some phenolphthalein, and stopper the flask with a cork stopper 

 through which passes a glass tube about 30 inches long and of about inch 

 internal diameter, having the lower end ground to a point on a grindstone. The 

 puri>ose of the tube is to serve as a reflux condenser. Place the flask and con- 

 tents on a steam bath and heat for thirty minutes. At the expiration of this 

 time the solution should be quite clear and show no alkali with the phenol- 

 phthalein. If the solution turns red during the boiling, showing that an insuffi- 

 cient quantity of stearic acid has been added at first, add more of that solution 

 until the color disappears, then several cubic centimeters in excess, and heat 

 twenty minutes longer. Remove the flask from the bath and, after cooling it a 

 few minutes, titrate with tenth-normal caustic soda. The difference between 

 the number of cubic centimeters of stearic acid solution added and the number 

 of cubic centimeters of caustic soda used to neutralize it is equivalent to the 

 total free alkali present. 



While the first flask is heating, weigh in a similar flask 2 grams of soap, 

 ;wld 50 cc of alcohol, and place on the steam bath. When the first test is 

 finished, calculate roughly the total alkali, assuming the total quantity to be 

 carbonate. Now add to the second flask sufficient 10 per cent barium chlorid 

 solution to precipitate the alkali found, 6 heat a few minutes, add phe- 

 uolphthalein, and titrate with tenth-normal stearic acid. The titratiou must 

 take place slowly and with thorough agitation of the liquid because the sodium 

 or potassium hydroxid reacts with the barium chlorid added and forms sodium 

 rliinrid and barium hydroxid. The latter is not very soluble in the alcoholic 

 liquid, and sufficient time and pains must be taken to insure its complete 

 neutralization by the stearic acid. Make a blank test on 50 cc of the alcohol, 

 since this frequently contains carbon dioxid, and add the amount of tenth- 

 iMirmul caustic soda necessary to neutralize the free acid in this quantity of 

 alcohol to the reading of the stearic acid burette in the second test. This 

 corrected reading gives the number of cubic centimeters of tenth-normal 

 stearic arid used to neutralize the caustic alkali in 2 grams of soap. The 

 difference between the total alkali found and the caustic soda will, of course, 

 give tin- carbonate. For example: To 2 grams of soap and 15 cc of teuth- 

 nonnal st-earic acid add :j.U < f truth-normal caustic soda to neutralize. 

 Then ]7 t cc 3.2 cc = 11.8 cc of tenth-normal stearic acid equivalent to total 

 free alkali. 



To ncntrali/.r the caustic soda in the sample treated with barium chlorid 

 4.1 cc of tenth-normal stearic acid was required. Fifty cubic centimeters of 

 the alcohol used required 0.2 cc of tenth-normal caustic soda, hence the total 

 Is 4.o cc. Since it requires 1..", cc of tenth-normal stearic acid to neutralize 

 free caustic alkali, 11.8 cc 4.3 cc = 7.5 cc of tenth-normal stearic acid required 

 t<> neutralize the carbonated alkali. 



".I. Anier. ('hem. So<-., I'.MK). 2'J :;'.):;. 



6 One cubic centimeter of tenth normal stearic acid corresponds to 0.0122 gram 

 BaCh 2H a O or 0.122 cc of a 10 per cent barium chlorid solution. 



