90 



results. The zinc-iron method works very smoothly, and some of the results are 

 quite as satisfactory as those obtained by the Schloesing- Wagner method. 



But, as stated above, we are mostly interested in the Gunning and Kjeldahl methods 

 for total nitrogen in the presence of nitrates. These methods have not given satis- 

 factory results in the past. There are some details in the manipulation of these 

 methods not described in Bulletin 107 which seem to tend materially to a closer 

 approximation of the true amount of nitrate nitrogen, such as quick covering of the 

 sample with enough salicyl-sulphonic acid to absorb all of the evolved nitrogen pxids, 

 sufficient time for thorough nitration of the acid, thorough cooling of the mixture 

 before adding the thiosulphate, and heating to a free boil before adding the mercuric 

 oxid or the potassium sulphate, respectively. We" find also that the tendency to 

 foam is very largely obviated by heating the flask containing the mixture in a boiling 

 water bath for an hour, or possibly less, prior to adding the thiosulphate. 



In view of the poor results obtained with nitric acid it seemed that the use of a 



Eure nitrate weighed directly into the digestion flask might prove much more satis- 

 ictory for determining the accuracy of the various methods. Our work following 

 this plan has given much better results than by using nitric acid as the source of the 

 nitrate. 



In the large majority of cases we have to do with mixed fertilizers containing a 

 nitrate. Any inaccuracies due to the water present in nitric acid or in the solution 

 of a nitrate could easily be obviated by evaporating to dryness in the digestion flask, 

 preferably in vacuo, after neutralizing when necessary to prevent the loss of nitric 

 acid. 



But even in the determination of an added nitrate the results leave much to be 

 desired. This is not only the case in this particular work, but has been a generally 

 recognized fact among fertilizer chemists for a long time. If the secret of success 

 lies in certain details of manipulation not commonly known, which make the method 

 reliable, these details should certainly be mentioned in the description of the method. 



Trescot says: 



I inclose results on neutralizing with soda and evaporating down, also on mixtures 

 of potassium nitrate and blood, and potassium nitrate and bone by the Gunning 

 modified method for nitrates and the Ulsch-Street method. These results only con- 

 firm my previous work on such materials with these methods. The zinc-iron method 

 is a failure in my hands. I never could get concordant results. If there is anything 

 more I can do, let me know and I will be glad to do it; only I do not wish to repeat 

 my work on the Ulsch-Street and Gunning modified methods, for after the most care- 

 ful checking for many years I am convinced that if handled properly, and on dry 

 materials, both methods will give all the nitrate present, 



DISCUSSION OP RESULTS. 



The opinions quoted and results reported show wide variations. By methods (c) 

 or (d) with and without organic matter, Robertson and Trescot alone get satisfactory 

 results; those of the other chemists are low, mostly impossible, in fact. This may 

 be due to heat generated by the acid and water, as many chemists think and as Rud- 

 nick's and Trescot's work on potassium nitrate seems to show. On the other hand, 

 Robertson's work shows no appreciable loss. An important question is, Must not 

 this possible loss from heat be reckoned with even with a comparatively dry sub- 

 stance? Even with potassium nitrate Rudnick falls far short of acceptable accuracy. 

 In view of these facts may not a too speedy application of heat in methods (c) and (d) 

 cause loss of nitrate vapors? It is a practice of some careful analysts to allow nitrate 

 samples to stand several hours after the thiosulphate or zinc dust is added. Hence, 

 recommendations are offered fixing a minimum time limit in methods (c) and (d). 



Method (g) as carried out by Bailey, Morrison, and Trescot gives good results; as 

 carried out by the other analysts uncertain and varying results, mostly far too low. 

 It must be noted, however, that to test the completeness of the reduction of nitric 

 acid to ammonia the distillation is made at first off magnesia and completed off soda, 

 except in Trescot's work, the amount of ammonia from each distillation being esti- 

 mated separately and the sum taken. It appears further from this process that the 

 distillation from magnesia is usually far from complete, giving in several instances 

 less than one-fifth of the total amount of ammonia; that is, less than one-fifth of what 



