The Determination of Dicyanodiamide and of Urea in Fertilizers
Journal of Industrial & Engineering Chemistry
533 arsenate is about 450' C. The fact that these two oxidations take place best a t the same temperature lead one t o think that possibly the lead oxide has played the role of a catalyst in this formation of lead arsenate; that is, that the litharge is first oxidized t o red lead, which in turn oxidizes the arsenious oxide to the pentoxide, or the lead arsenite to lead arsenate. From this it would follow t h a t the temperature a t which a catalyst for oxidation would work best would be t h a
... temperature a t which it is most easily oxidized t o the higher oxide. Then in selecting a catalyst for any particular oxidation, that catalyst should work best which is oxidized most easily a t that temperature a t which the desired oxidation is niost easily effected. ' i S U M M A R Y 1-Lead arsenate is produced by roasting a mixture of litharge and white arsenic at the proper temperature. 2-The best temperature for roasting is about 450' C. 3-The first part of the oxidation is very rapid, while 4-The possibility of catalytic action has been later i t becomes very slow. pointed out. DICYANODIAMIDE I n the course of work upon cyanamide about four and a half years ago, i t became necessary t o find a more rapid method for the determination of dicyanodiamide in cyanamide 2nd mixed fertilizers. A t t h a t time t h e author and Mr. Berbom obtained the same dicyanodiamide-silver picrate complexes as have recently been described by Harger.2 The results of this work are published at this time as confirmatory 2nd supplementary t o those of Harger. For the purpose of rapidity, a volumetric determination is desirable. Such a determination of dicyanodiamide in the mono-compound is practically impossible on account of the large excess of silver salt necessary in its preparation. Attention was therefore directed t o the double complex, silver picrate dicyanoguanidine, CBH2(N02)sOAg.2C4H2N4. Under certain conditions the di-compound is so insoluble, and its conversion into the mono-compound according t o the reaction C~H~( N O Z )~O A~.~C~H~N~ + CsHz(N02)30Ag = ~C~H Z ( N~Z )~O A~. C~H~N~ is so slow that the amount of standard silver solution used can be made the basis of a volumetric method. The conditions necessary involve dilute solutions, low temperature, and a large excess of picric acid.