1885.] Limited Hydration of Ammonium Carbamate. 



391 



In order to gain some idea as to the effect which temperature 

 might have npon the action, two equal volumes of an arbitrary solu- 

 tion of ammonium carbamate were taken and kept in sealed vessels, 

 one at the temperature of the room — about 15° C, and the other in 

 melting ice. After about five hours the solutions were examined by 

 the hypochlorite method, taking care to keep the apparatus in each 

 case as nearly as possible at the respective temperatures. 



Solution at 0° C. gave 68 '0 c.c. N (corr.). 

 15 „ 79-4 



Similar pairs of experiments were made with another solution at 

 stated intervals, equal volumes being measured out in the first 

 instance and then subjected to the respective temperatures in sealed 

 vessels. 



After 30 minutes solution at 0° gave 63 *7 c.c, solution at 15° gave 76 *2 

 ,; lhour „ „ 73-0 „ „ 83-2 



2 hours „ „ 74'0 „ „ 88*9 



„ 4 „ „ „ 76-3 „ „ 90-6 



The hydration is therefore, in all cases, less at the lower tempera- 

 ture. 



The minimum hydration will probably occur at a sufficiently low 

 temperature, and when the substances are present in equal molecular 

 proportions. A mixture was made of 0*6199 gram ammonium car- 

 bamate with 01424 gram of water — corresponding almost exactly to 

 equal molecular weights. This mixture was kept in a sealed tube 

 placed in a block of ice for 18 hours, when it may be safely assumed 

 that the equilibrium state was arrived at. It was then examined by 

 the hypochlorite method (the apparatus being kept at about 0° C. 

 throughout), and yielded 95*90 c.c. of nitrogen (corrected). Theory 

 for total nitrogen requires 1771 c.c, so that the hydration is repre- 

 sented by 0*0830. 



Probably, at a sufficiently low temperature, the hydration would be 

 practically nil, when the substances are present in molecular pro- 

 portions — i.e., ammonium carbamate and water would practically not 

 combine at all — resembling the cases of phosphorus trichloride and 

 chlorine, &c, at sufficiently high temperatures. 



IV. Dehydration of Normal Ammonium Carbonate. 



The salt was prepared by the method of Divers.* About 5 — 6 grams 

 of it were dissolved in water, and the solution made up to 100 c.c. (A). 

 Portions of this solution were diluted to -J (B) and ^ (C). After 

 two days — 



* " Chem. Soc. Jour.," 23, 179. 



