( 297 ) 



On Water as a Constituent of Salts. 1 . In the case of Sulphates. 

 By Thomas Graham, F. R. S. Edin., V.-Pres. of the Phil. Soc. 

 of Glasgow, &c. 



(Head 5th January 1835.) 



It may be useful to distinguish some of the functions which 

 water is already admitted to discharge in the constitution of 

 hydrated salts. 



Every amphigene ammoniacal salt contains an atom of wa- 

 ter, and cannot exist without it. The state of combination of 

 the water is peculiar, and has been represented by supposing 

 that the elements of ammonia unite with the hydrogen of the 

 water, and form a new compound radicle, to which the name 

 Ammonium is given, while the oxygen of the water unites with 

 this radicle, and produces oxide of ammonium. Hence nitrate 

 of ammonia, in which there exist the elements of one atom of 

 nitric acid, of ammonia, and of water, is viewed as anhydrous 

 nitrate of the oxide of ammonium, and corresponds with nitre 

 or the nitrate of the oxide of potassium. But it is not the ob- 

 ject of this paper to discuss particularly the state of water in the 

 ammoniacal salts. 



We have it often in the crystals of salts, united by a feeble 

 affinity, and known under the name of water of crystallization. 

 The number of atoms of water with which some salts unite, in 

 crystallizing from a state of solution, is affected by temperature, 

 and other slight causes. This water is commonly viewed as a 

 constituent of salts which is not essential, owing to the facility 

 with which it may in general be expelled by heat, and also to 

 VOL. XIII. part. i. p p 



