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On Water as a Constituent of Salts. 1. In the case of Sulphates. 
By Tuomas Granam, F. B.S. Edin., V.-Pres. of the Phil. Soc. 
of Glasgow, &c. 
(Read 5th January 1835.) 
Ir 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. Pp 
