TiCHBORNE — Oil the Dissociation of Molecules in Solution. 233 



In the case of a volatile base and acid siicli as carbonate of ammonium, 

 •we bare a partial dissociation, attended with both loss of acid and 

 base, btit -wliich fi^om the tendency to assimilate the acid molecule II' 

 H A" is productive of a curious decomposition. The two following ex- 

 periments will illustrate this in a striking manner. 



They are perfoiTaed with the most permanent of the ammonium 

 salts, the sidphate (jS'HDoSO^, and the most unstable, viz. (xs'Il4)2C03, 

 the normal carbonate. We find that at a very slight increase of tem- 

 perature the sulphate molecide is no longer permanent. Crystals of 

 sulphate of ammonium were taken which were perfectly pure and neutral. 

 A porcelain crucible was filled with these crystals, and a sufficient 

 quantity of water was added to moisten them. The crucible was 

 placed in a water bath provided with a thermometer, and covered with 

 a beaker, a piece of blue litmus was placed upon the surface of the 

 moistened sulphate, and a piece of red litmus in the beaker. At a 

 temperatm-e 16° C. a slight decomposition took place, but at 20° C. 

 the tension of the gaseous base was so raised that rapid decomposition 

 Bet in, the litmus paper in the salt becoming red fi'om the formation 

 of j!^Il4 HSO^ and the Htmus paper in the beaker, which was originally 

 red, becoming blue from evolved ammonia. 



Water is essential to such a phenomenon, and no decomposition can 

 be perceived with the chy salt, under such a condition, mobility of the 

 atoms being essential. 



Carbonate of ammonium jSTH^ CO3 was fonned, by treating ordinary 

 carbonate with ammonia, and the result was a moist salt, but still 

 in the form of a powder. It was placed in a vessel the sides of which 

 were perfectly cleaned : this vessel was then surrounded with a freezing 

 mixtiu'e of a considerable power, and at a temperatui'e of about 4° C. it 

 became nearly odourless, and at a much lower temperature perfectly so. 

 Thus we find that the most permanent salt of ammonia is in a state of 

 tension thus : 



^iloleciile of Sulphate of 

 Ammonium. 



Molecule of Sulphate of Ammonium dissociated by heat into two molecules. 



R. I. A. PROC, SER. n., vol.. II., SCIEXCE. 2 I 



