1912] Lipman-Sharp: Phenoldisulphotiic Acid Method 35 



error, and to establish the method on a firmer basis. Our results 

 as above outlined show that losses of nitrates are induced by 

 the presence of NaCl and NaoSO^, and such losses are indeed 

 hard to avoid when working with "alkali soils." Even the 

 suggestion of Chamot that AgSO^ might be used to precipitate 

 chlorides would seem, from our results, not to be useful, since 

 the addition of sulfate to the solution would accomplish very con- 

 siderable losses itself, even if the silver sulfate can be obtained 

 nitrate-free, which Chamot claims is seldom the case. So that while 

 we deem it unsafe in the presence of considerable quantities of salts 

 containing chlorides and sulfates to determine nitrates by the 

 phenoldisulphonic acid method and M^ould therefore recommend 

 the Street modification of the Ulsch method in such cases, it is 

 likewise clear that many of the nitrate determinations made 

 in soil laboratories, as is especially the case in soil bacteriological 

 work, would not be interfered with by salts. In such cases the 

 method can be safely depended on if potash alum, aluminum 

 cream, and bone black are not used to coagulate clay and or- 

 ganic matter, since they have been found in the researches above 

 described to be productive of very serious errors. We recom- 

 mend as a substitute for these coagulating agents the oxide of 

 lime in its chemically pure state, to be employed in accordance 

 with the method above given. The losses of nitrates sustained 

 through its use have been shown to be very small in the work 

 above reported, and it may be employed by grinding the soil 

 with water or by direct addition to the muddy suspension pre- 

 pared from the soil. 



Other sources of loss such as those brought about through 

 the sterilization of controls in the autoclave are unavoidable. 

 They have been found at times to be distinctly appreciable, and 

 especially in the presence of considerable quantities of organic 

 matter. It is further of the greatest interest to learn, from the 

 experiments above described, of the action of the anion of the 

 salts employed in our studies and the losses of nitrates occurring 

 on the water bath from solutions being evaporated there when 

 either NaCl or NajSO^ is present. 



We should also make mention here of our attitude toward 

 the use of NH^OH instead of KOH, which was found superior 



