184 Notices of the Labours of Continental Chemists. 



been obtained with other bases, such as soda, barytes, magne- 

 sia, lime, and the oxides of zinc and lead. On the contrary, 

 the heat developed by each base is peculiar to itself; and, 

 consequently, the same acid gives different elevations of tem- 

 perature, with equivalents of different bases. To take, as an 

 example, the nitric acid, which also produces very nearly the 

 mean quantity of heat given by all the acids, the following 

 numbers express the increments of temperature obtained on 

 combining the same quantity of it with each base: — magne- 

 sia, 8*1 °; lime, 7*2°; barytes, 6-9° ; potash, 6-8°; soda, 6*5°; 

 ammonia, 5'6° ; oxide of zinc, 4>'8° ; oxide of lead, 4*2° ; oxide 

 of silver, 3-2°. The numbers for barytes, potash, soda and 

 ammonia, are strictly comparable with one another (except a 

 slight correction for differences in the specific heats of the so- 

 lutions) ; but in the case of the other bases, an absorption of 

 heat, unknown in amount, takes place in consequence of their 

 conversion from the solid to the fluid state. Hence the num- 

 bers for these bases are all below the truth. 



Two singular anomalies are described as occurring in the 

 combinations of the peroxide of mercury with the hydracids, 

 and in those of the hydrocyanic acid with the bases. 



In confirmation of the second law, the author adduces' a 

 series of experiments, which prove, that during the conver- 

 sion of a neutral into a supersalt no heat is produced. Thus 

 while the normal development of heat occurs when a solution 

 of caustic potash is neutralized by oxalic acid, the subsequent 

 additions, first of one, and afterwards of two more atoms of 

 the same acid, so as to convert the neutral oxalate into the 

 binoxalate, and the latter again into the quadroxalate of pot- 

 ash, are not accompanied by any change of temperature in the 

 solutions. In testing the accuracy of this law, it is necessary 

 to select examples where all the compounds are soluble in 

 water, otherwise the heat arising from the formation of preci- 

 pitates would interfere with and complicate the result. 



The second law does not extend to the case of the conver- 

 sion of neutral into basic compounds, — a part of the subject 

 which the author has carefully investigated. 



XXIX. Notices of the Results of the Labours of Continental 

 Chemists. By Messrs. W. Francis and H. Croft. 



[Continued from p. 49.] 



Preparation of Urea. 



HPHE usual method of preparing urea by precipitating it from 



urine by means of nitric acid, is attended with great expense 



of time and material. Prof. Liebig has recently published the 



