1889.] On Salts of a Base containing Chromium and Urea. 327 



The direct decision of such an apparently simple matter as the 

 composition of the chief initial product of the reaction has, up to the 

 present time, been found to be impossible. No reagent or mixture of 

 reagents has been discovered which at once dissolves any excess of 

 materials used and the other products of the reaction, without pro- 

 ducing some change in the composition of the chief product. 



A careful examination of the reaction between chrornyl dichloride 

 and urea was made by taking known weights of the materials, col- 

 lecting and measuring the gaseous products, and after the addition 

 of water to the residue, estimating the dichlordichromate produced, 

 as well as the other products which pass into solution. The dichlor- 

 dichromate was then calculated as dichlortetrachlorocb.ro mate. 

 Without going into a mass of detail, it may be stated that the results 

 of the examination gave numbers very nearly agreeing with the 

 equation 



1300 (NH 2 ) 2 + 9O0 2 C1 2 = { (CON 2 H 4 )i 2 Cr 2 j + Cr 2 Cl 6 



With regard to the preparation of these substances, it may be well 

 to note that the reaction of chromyl dichloride on urea succeeds best 

 in narrow test-tubes, working with about 3 grains of urea. On a 

 larger scale the reaction becomes very difficult to control, and decom- 

 position more or less complete is very liable to ensue. On the other 

 hand, unless the reaction is fairly vigorous and the temperature 

 allowed to rise, little or none of the compound is produced. 



A considerable amount of time has been taken up in attempts to 

 prepare this class of compounds by some modification of the above 

 process which should present less complexity, and thus offer rome 

 hope of arriving at their constitution. Passing over the unsuccessful 

 attempts, it was discovered that the dichromate of the base may be 

 obtained by the action of chromic acid on urea. In the month of 

 September of last year three separate portions of nearly equal 

 weights of urea and chromic anhydride were dissolved in a small 

 quantity of cold water, the solutions covered with filter-paper, and 

 allowed to stand at the ordinary temperature. 



On examination in March the solutions had changed colour, become 

 quite thick from evaporation, and on addition, of water a small quan- 

 tity of sparingly soluble green crystals were found to be left. These, 

 when separated and recrystallised from hot water, had all the cha- 

 racters of the dichromate of the base, and gave on ignition 41 '32 per 

 cent, of Cr 2 3 ,' against 41 '43 as required by theory for the dichro- 

 mate. It was subsequently found that the dichromate may be formed 

 in some quantity by evaporating the aqueous solutions of the mixed 



