ROSE ON THE ANHYDROUS SULPHATE OP AMMONIA. 559 



III. The Deliquescent Salt. 



This salt, as already mentioned, is contained in the solution 

 from which the parasulphat-ammon has crystallized ; if this be 

 evaporated to dryness over sulphuric acid in vacuo, imperfect 

 crystals, or crystalline crusts only are obtained, which attract 

 moisture from the air, and eventually deliquesce ; it is very diffi- 

 cult to obtain this salt perfectly free from parasulphat-ammon ; 

 it is indeed more soluble, but the parasulphat is not very diffi- 

 cultly so, which renders it impossible to separate them when 

 operating on small quantities ; but in larger quantity I effected 

 their separation in the following manner : I allowed the solu- 

 tion, which had been evaporated to dryness in vacuo over sul- 

 phuric acid partially to deliquesce by exposure to the air ; or 

 added a few drops of water to it, left them for some time in 

 contact, and then evaporated the small portion of the salt [dis- 

 solved], again to dryness, as before, and employed it for analysis. 

 If the solution of the salt contains parasulphat-ammon, and 

 if it has been evaporated very slowly over sulphuric acid, but 

 not in vacuo, the crystals obtained from it become, in a moist 

 state, very readily acid ; the crystals of the parasulphat-ammon 

 must therefore be picked out as much as possible from the 

 mass evaporated to dryness, then the deliquescent salt must be 

 dissolved in water, and carbonate of barytes added to the solu- 

 tion to saturate the fi-ee acid, and lastly, the solution must be 

 again evaporated in vacuo. 



The crystals of the salt are too indistinct to admit of their form 

 being determined, and they are usually mere crystalline crusts, 

 and any crystals which may be observed with bright faces are 

 par asulph at-ammo n , 



The solution of this salt instantly precipitates solutions of 

 barytes ; but, as happens with the solution of sulphat-ammon, 

 not nearly the whole of the sulphuric acid is thrown down in 

 the state of sulphate of barytes. When hydrochloric acid is 

 added to the solution, more sulphate of barytes is precipitated 

 in the cold, than without such addition ; a solution of chloride 

 of strontium produces immediate precipitation in the solution of 

 this salt only when very much concentrated ; this distinguishes 

 the solution from that of sulphat-ammon. If equal quantities 

 of both salts are dissolved in similar quantities of water, both 

 the solutions arc not precipitated by a dilute solution of a salt 



