APPENDIX H 149 



liquor by filtration with ?, filter pump. The silver nitrite is redis- 

 solved in the smallest possible quantity of hot water, allowed to cool, 

 and the crystal mass again separated by means of suction. The 

 crystals are then quickly dried in a water bath and preserved in a 

 tightly stoppered bottle in the dark. 



5. Standard colorimetric solution. This may be prepared by dilut- 

 ing 10 cc. of the above standard sodium nitrite solution (4) to about 

 80 cc., adding 16 cc. of the nitrite reagent (3) and making up to 

 100 cc. It must be prepared at the same time as the test solutions. 

 This colorimetric standard has the strength of one part N0 2 per mil- 

 lion, and solutions of other strengths may be similarly prepared when 

 necessary, using the same quantity of reagent. 



ANALYTICAL PROCESS 



Dilute a measured volume of the solution, if necessary, to about 

 40 cc.. add 8 cc. of the nitrite reagent (3), and dilute to 50 cc. Develop 

 the color of the standard solution at the same time. Allow the solu- 

 tions to stand fifteen minutes and then determine their relative 

 strengths in the colorimeter or by direct comparison by any of the 

 other colorimetric procedures. 



