436 Dr. Thomson on ' [Dec. 



any attention without being struck with some new and unex- 

 pected phenomena. Indeed our knowledge of sahne combina- 

 tions and of the limits within which these combinations are 

 confined, is so important that we are not prepared to reason 

 generally on the subject. Compounds are perpetually presenting 

 themselves which are at apparent variance with our preconceived 

 notions. For example, what opinion is more firmly established 

 than that the saline compound of sulphuric acid and soda cannot 

 crystallize unless it be combined with a considerable quantity of 

 water? Yet I have lately met with this acid and base combined 

 in definite proportions and in well-formed crystals totally desti- 

 tute of combined water. 



The muriatic acid of commerce is never free either from sul- 

 phuric acid or iron. On that account I am in the habit of pre- 

 paring muriatic acid for the purposes of analysis by passing a 

 current of muriatic acid gas through distilled water till the liquid 

 refuses to absorb any more. The common salt from which the 

 muriatic acid gas is evolved is put into a large retort, and the 

 requisite quantity of sulphuric acid of commerce to decompose it 

 is poured in at intervals through the tubulated opening in the 

 retort. The retort is heated by a lamp. 



By this process a vast quantity of gas is evolved at first ; but 

 it gradually diminishes, and at last ceases altogether long before 

 the whole of the common salt is converted into sulphate of soda. 

 Indeed this complete decomposition cannot be effected without 

 a degree of labour and a repetition of so many processes, that I 

 find it not worth while to prosecute it beyond a certain point. 

 There remains in the retort an indurated, white, and very sour 

 tasted salt, which I dissolve out by filling up the retort with 

 water, and digesting it on the sand-bath. The difficult solubi- 

 lity of this sahne residue is so considerable that repeated diges- 

 tions and a great deal of water are necessary to remove it out of 

 the retort. If the first solution obtained in this manner, which 

 is exceedingly acid, containing a great excess of sulphuric acid, 

 be concentrated on the sand-bath and set aside for crystalliza- 

 tion, the first crop of crystals formed is usually very similar in 

 shape to glauber salt ; but they are much firmer and heavier, and 

 have an exceedingly acid taste. These crystals do not always 

 appear, and I have not ascertained the circumstances upon which 

 the appearance depends ; though it is probably connected with 

 the proportion of excess of acid which the liquid contains. But 

 I have procured them several times successively in the circum- 

 , stances just described, and see no reason to doubt that other 

 chemists, by proceeding in the same manner, will be equally for- 

 tunate. These crystals constitute a new anhydrous salt, which, 

 from its constitution, I shall call sesquisulphate of soda. I shall 

 give a short account of the properties and analysis of this salt. 



