ALKALIMETRY. 241 



streaks which are made with the liquid upon litmus- 

 paper, remain red after drying. 



The number of measures of acid employed is then 

 observed, and the whole of the test-acid is diluted with 

 so much water, that exactly 100 measures are required 

 to neutralize 5 grms. of pure carbonate of soda. This 

 stock of test-acid is preserved in a well-stopped bottle. 

 It indicates immediately the percentage of caustic or 

 carbonated alkali in a specimen of potashes or soda, 

 provided that a quantity of the sample be employed, 

 which is equivalent to 5 grms. of carbonate of soda. 



100 measures of test acid saturate 5.000 grms. of oarb. of soda. 

 100 " " " 2 935 " of soda. 



100 " " " 6.487 " of carb. of potassa. 



100 " " 4.421 " of potassa. 



So that if 6'487 grms. of a sample of potashes be 

 taken, the number of measures of acid employed will 

 express, directly, the percentage of carbonate of potassa, 

 or if 4.421 grms. be used, of anhydrous potassa, con- 

 tained in the specimen. 



Instead of sulphuric acid, pure crystallized oxalic 

 acid may be very conveniently employed for preparing 

 the test-solution. An equivalent of the acid (63 grms.) 



Fig. 29. 



is introduced into a flask of 1 litre capacity, which is 

 then two-thirds filled with water ; the acid is allowed 

 21 



