Mineral Waters. 269 



we may be certain that the lead is precipitated 

 by sulphuric acid. A combination- of 'the nitric 

 acid in water cannot be discovered, except by 

 examining the remainder of the water after a 

 gentle evaporation and crystallization. From 

 the experiments of those who have examined 

 waters of this kind, it is always found to be con- 

 tained in the state of nitre, which may be known 

 by its crystals ; but we must never conclude a 

 salt to be nitre, unless it deflagrates with com- 

 bustible substances. If evaporation shows that 

 the nitric acid is united with an earth, it will be 

 proper to add pure alkali, which will form a 

 nitre that may be separated by crystallization. 

 The alkali used should be potass, as none else 

 can be depended upon. The fixed alkali is said 

 to be often combined with the sulphuric, nitric, 

 and muriatic acids. We know that it is often 

 in a state of combination with the muriatic, and 

 somatimes with the nitric acid ; but its com- 

 binations with the sulphuric are more doubtful. 

 The experiments which have been supposed to 

 prove the presence of sulphat of soda in mineral 

 waters, have in reality proved the presence of 

 sulphate of magnesia; but the only way of dis- 

 covering the alkali is by evaporation and crystal- 

 lization. If, indeed, other experiments show 

 that this is neither saturated with an earth nor a 

 metal, we must conclude it to be saturated with 

 an alkali ; but evaporation is the best method, as 

 it will show whether the alkali is fixed or vola- 



