APPENDIX (J 147 



AN AL YT I C' A L PROCESS 



Evaporate 50 cc. or other convenient quantity, depending upon the 

 amount of nitrate present, to dryness in a porcelain dish on a water 

 bath, removing the dish as soon as it is completely dry. Add 1 cc. 

 of the phenoldisulphonic acid reagent (1) and stir thoroughly with 

 the rounded end of a glass rod so as to loosen the residue and bring 

 the acid well in contact with every portion of it. The time of action 

 on the nitrate should be about ten minutes. At the end of this time 

 the acid is diluted with about 15 cc. of water and made alkaline 

 with ammonium hydroxide (2), a yellow color being developed when 

 the solution becomes alkaline. This is then diluted to 50 cc. or 

 100 cc. and compared in the colorimeter with the standard colori- 

 metric solution (4). If the color is too intense for direct compari- 

 son with this standard, an aliquot portion may be taken and diluted 

 to definite volume and the strength of this determined. 



