350 EXPERIMENTS ON THE RELATION 



experiments very carefully conducted ; and we shall find, that 

 though this salt, is not, perhaps in strict chemical language, 

 deliquescent, yet it is capable of absorbing or attracting from 

 the atmosphere a very notable portion of water. This, how- 

 ever, may be totally expelled, by keeping the salt for a short 

 time in a temperature of from 200° to 300° of Fahrenheit, 

 when it resumes exactly its pristine weight. 



Pulverised sal ammoniac was desiccated in a platina capsule, 

 at a heat somewhat below that of its sublimation. It was then 

 found to weigh 49 gr. I placed the capsule on a shelf in my 

 apartment. On re-weighing it, at the end of two days, the 

 salt was found to have become heavier by 3.1 gr., which 

 amounts to more than six parts in the hundred. Sal ammo- 

 niac from gaseous combination exhibits the same phenome- 

 non ; and probably, from the extreme comminution of the 

 powder, to a still greater degree. It even becomes pasty. The 

 quantity of this adhering or hygrometric water, will vary no 

 doubt with the weather or climate, as is the case with muriate 

 of soda *. 



It may be said, Since our sole object in decomposing sal am- 

 moniac, by metallic laminas, is to obtain from its acid consti- 

 tuent the water which it is supposed intimately to contain, and 

 to carry into that salt ; why not employ directly dry muriatic 

 acid gas, in such researches ? My only answer is, that in de- 

 siccated sal ammoniac, we conveniently find the acid in a state 



hygrometrically 



* In clear frosty weather, or in a very dry apartment, where muriate of lime 

 would crystallise, the ammoniacal salt acquires weight very slowly. Fifty grains 

 of that from gaseous combination, just heated in a platina capsule, to near its 

 subliming temperature, being put into the scale of a sensible balance, became 

 heavier by half a grain in two minutes ; after which, in the above circumstances, 

 no further absorption of moisture was perceptible for an hour. The experiments 

 detailed in the text were made, when the air was considerably loaded with mois- 

 ture. 



