316 Dr Ogden on Saline Crystallization. 



Table I. 



Carbonate of soda. Oxalate of ammonia. 



Sulphate of soda. Sulphate of magnesia and ammonia. 



Tartrate of soda and potash. Sulphate of magnesia. 



Biborate of soda. Muriate of lime. 



Acetate of soda. Muriate of bary tes. 



Phosphate of soda. Acetate of lead. 



Ferrocyanate of potash. Sulphate of iron. 



Supersulphate of alumina and potash. Sulphate of zinc. 



Bisulphate of potash. Sulphate of copper. 



Tartrate of potash and antimony. Bichromate of potash. 

 Nitrate of ammonia. 



Table II. 



Muriate of potash. Bichloride of mercury. 



Nitrate of potash. Nitrate of barytes. 



Sulphate of potash. Muriate of ammonia. 



Chromate of potash. Sulphate of ammonia. 



Chlorate of potash. Sulphate of magnesia and potash. 

 Nitrate of lead. 



In the progress of these experiments I could not avoid ob- 

 serving, that the principal characteristic difference between these 

 two sets of salts was, that the first contain water of crystalliza- 

 tion, whereas the second are anhydrous. So generally true is 

 this, that it was with some surprise that I found bichromate of 

 potash, an anhydrous salt, to form an exception. Of all the rest 

 of the salts in the first table, the crystals are hydrates. In the 

 second table there are two exceptions, sulphate of ammonia, and 

 sulphate of magnesia and potash, both of which are crystalline 

 hydrates. These three exceptions (and many others may yet 

 be found) annul the distinction between hydrated and anhy- 

 drous salts, and invalidate any general rule which might be 

 founded on it. v 



Whilst operating on sulphate of soda, I frequently observed- 

 a deposition of a portion of the salt, in the form of brilliant 

 transparent crystals, which became white and opaque when 

 crystallization was induced in the remaining Hquid. This phe- 

 nomenon is described by Mr Faraday in the Journal of Science, 

 vol. xix. ; he finds the crystals to contain eight only, instead of 

 ten, atoms of water of crystallization. Mr Faraday refers to 

 their production in closed vessels only. I have generally experi- 

 mented with open vessels, and all the instances I have seen have 



