040 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



INVESTIGATIONS ON THE TRANSFORMATION AND UTILIZATION OF NITROGEN 



COMPOUNDS. 



Next in importance to the fixation of nitrogen is the transforma- 

 tion of the different nitrogen-containing substances in order to make 

 them more useful in agriculture, in explosives, and in the arts. Dur- 

 ing the past year the laboratory has conducted a number of investiga- 

 tions in this connection. Since many of them are described in the 

 re2:)ort on the fixation and utilization of nitrogen, only the more im- 

 portant ones will be referred to in this report. 



SYNTHESIS OF UREA. 



Urea is one of the most attractive nitrogen-containing materials 

 fi'om the fertilizer standpoint, but at the present time its cost for 

 such use is prohibitive. The laboratory has developed on a semi- 

 technical scale a process for the production of urea from ammonia 

 and carbon dioxide which seems to possess possibilities of ultimately 

 3'ielding this material at fertilizer prices. The process could be 

 very advantageously operated in conjunction Avith a direct synthetic 

 ammonia plant employing the water-gas reaction for hydrogen, 

 since waste carbon dioxide would in that case be available. The 

 results of the investigation on this process Avere published in the 

 July, 1922, issue of the Journal of Industrial and Engineering 

 Chemistr}'. 



OXIDES OF MTKOCKX. 



Oxides of nitrogen are obtained as the direct product in the arc 

 process of nitrogen fixation, in the conversion of ammonia nitrogen 

 to nitrate nitrogen by oxidation, and also in various nitration proc- 

 esses. At the present time the recovery of oxides of nitrogen from 

 the dilute gas mixtures obtained in all these processes requires very 

 large and expensive absorption systems. Furthermore, the product 

 is a dilute acid, the further concentration of which is also expensive. 

 The importance of developing a process by which the final product 

 can be directly obtained in suitable form, particularly as concen- 

 trated nitric acid and dry nitrogen tetroxide. is therefore evident. 



The laboratorj^ has made considerable progress in the solution of 

 this problem during the past year. The two main phases of this 

 problem are the separation of the oxides of nitrogen from the ac- 

 companying gas and the conversion of the concentrated teases thus 

 obtained into concentrated nitric acid. The utility of silica gel in 

 effecting the separation as well as for the production of dry nitrogen 

 tetroxide has been shown, but further work is required to determine 

 the optimum conditions of operation of this new process. Work was 

 also begun on the direct production of concentrated nitric acid from 

 concentrated oxides of nitrogen. In connection with the possibility 

 of producing concentrated or fuming nitric acid from extremely 

 dilute oxides of nitrogen, so dilute that they are now wasted, a careful 

 study of the reaction between ozone and nitrogen tetroxide was made. 

 It was found that the conversion to nitrogen pentoxide is rapid and 

 c[uantitative. The present high cost of producing ozone, however, 

 is a limiting factor in commercially applying this process. 



