[ Bio ] 



CHAPTER CXXXIIL 



THE STANDARD ACID AND AI,KAU. 



'"PHE strength of the Sulphuric acid to be used for the 

 estimation of nitrogen, should be determined once for 

 all and noted on the jars or bottles. This is done in the 

 following way : 



Twenty cubic centimetres of the Sulphuric acid should 

 be taken by means of a pipette into a clean beaker; then 

 another 20 c. c. into another beaker; and a third quan- 

 tity of 20 c.c. in a third beaker. Ten times as much distilled 

 water should be added to each, i. <?., about 200 c.c. A few 

 drops of dilute Hydrochloric acid should then be added to 

 each. The contents of the beakers are then successively 

 boiled, and when boiling just commences, solution of Barium 

 chloride in a boiling state should be gradually added, and the 

 contents of the beaker stirred with a glass rod, until all preci- 

 pitation ceases. The liquid is to be kept near the boiling 

 point for sometime, and then covered up and left in a sand-bath. 



1.392. The liquid should then be brought to the boiling 

 point and filtered, the next day, through Swedish filter-paper ; 

 the precipitate on the paper being washed several times with 

 hot water, also the residue of the precipitate in the beaker. 

 When all the precipitate has been transferred into the 

 filter, the funnel with the precipitate is to be covered up with 

 a piece of paper and left on the water oven to dry. One pre- 

 caution should be always taken before transferring the contents 

 of a beaker into a filter, etc.: the edge of the beaker should be 

 greased and a glass rod should be used while pouring the con- 

 tents of the beaker into the filter. The filter-paper should be 

 moistened with water blown out from a wash bottle before 

 the liquid is poured on to it. 



1.393. Next day, the precipitate is to be carefully scraped 



