118 Gooe/i and Gruener — Method for the 



increasing the strength of the sulphuric acid that it was acted 

 upon by hydriodic acid with the consequent unregistered 

 escape of products of decomposition. 



The endeavor to substitute a process essentially similar in 

 principle, in which hydrochloric and antimonic acids should 

 replace the sulphuric and arsenic acids proved likewise un- 

 successful. 



Abandoning therefore all attempts to so arrange the process 

 that the oxidizing action of the nitrate should be registered in 

 the residue, search was made for a reagent which should be 

 capable of inducing easy decomposition of nitrates (after the 

 manner of ferrous salts in acid solution) and yet (unlike ferrous 

 salts) should be so readily restored to its primitive condition 

 that the products of the oxidizing action of the nitrate should 

 finally pass entirely to the distillate and be registered there. 

 We have found the desired combination of qualities in manga - 

 nous chloride dissolved to saturation in concentrated hydro- 

 chloric acid. This reagent is acted upon but slowly by nitrates 

 at the ordinary temperature, but upon warming the nitrate 

 begins at once to decompose with the formation of a higher 

 chloride of manganese and liberation of nitric oxide. Ulti- 

 mately if the heating is continued the chlorine of the higher 

 chlorides is evolved and manganous chloride remains. During 

 the process of heating the color of the solution passes from the 

 original characteristic green through darker shades to black 

 and returns by the reverse changes to the original tint. The 

 decomposition of the nitrate extends under the conditions to 

 the last traces, but the breaking up of the nitrates with the 

 formation of the higher chloride, does not take place com- 

 pletely in the presence of water amounting to more than a 

 third of the volume of the solution, and an action already estab- 

 lished in strong acid is reversed by the addition of a large 

 amount of water. Chlorates, peroxides, and other substances 

 which liberate oxygen or chlorine when in contact with strong 

 hydrochloric acid induce similar phenomena, but in the absence 

 of such other substances the reaction serves to detect nitrates 

 when present in fairly small amounts (perhaps one part in 

 sixty thousand) as shown in the accompanying table : 



KN0 3 MnCl 2 . 4H 2 Color 



taken. 



in strong HC1 



developed. 



0*01000 grm. 



10 



cm 3 



Black. 



0-00500 



5 





Black. 



o-ooioo 



5 





Dark brown. 



0-00050 



5 





Dark green. 



0-00025 



5 





Deepened tint 



0-00015 



5 





Deepened tint. 



0-00005 



5 





None. 



o-ooooo 



5 





None. 



