the Laws of Affinity. 347 



muriatic, or tartareous acid. When the decomposition is 

 canied to its boundary, it stops, whatever may be the quan- 

 tity of the acid opposed ; and if the quantity is not too great 

 to prevent crystalhzation, or if the excess be expelled by heat, 

 an acidulous sulphat, which forms crystals permanent in the 

 air, will be obtained by solution and evaporation. 



3d, How could the illustrious Bergman deviate from the 

 route traced out to him by observation ? His own experiments, 

 even, prove that the acid, which is superabundant in the aci- 

 dulous sulphat of potash, exercises its affinity ; that it is in 

 combination ; and that it acts in the ratio of its quantity : 

 for he says, that if sulphuric acid be added to the acidulous 

 sulphat of potash, this salt dissolves, and loses its property of 

 crystallizing ; that this excess of acid can with difficulty be 

 expelled even by distillation in a retort ; and that, to produce 

 this effect, the saline combination must be fused in a crucible, 

 or be exposed several times to the action of very pure alcohol. 



4th, The limit, then, which Bergman gives to the action 

 of acids on the acidulous sulphat is ideal. This sulphat ex- 

 hibits the same phaenomena as all the salts which are capable 

 of resisting, to a certain degree, the action of an excessof acid 

 ®r base (Art. V. No. 4.), as well as the action of another 

 acid or a foreign base. The only difference there is between 

 them in this respect depends on the force of cohesion which 

 may act more or less to produce crystallization, and which is 

 proper to certain proportions of acid and base ; probably a 

 consequence of the figure assumed by the moleculae of their 

 combination. 



5 th, When an acid has the property of forming a preci- 

 pitate by combining with a base, it is concluded that it has 

 more affinity for that base than for the acid with which it 

 was first united, without examining how far the new acid 

 may have operated the decomposition, and without reflecting 

 that an opposite decomposition takes place by a simple change 

 of proportions, and might consequently conduct to an opposite 

 conclusion. 



Thus, as the tartareous acid has the property of forming, 

 with potash, an acidulous salt very little soluble, and con- 

 sequently forms a precipitate with all salts having a base of 



X X 2 potash. 



