of Mineral Waters. 22\ 



a Oxygen and nitrogen exist in the greater number of spring 

 waters in the proportions constituting atmospheric air ; the pro- 

 portion of nitrogen is, however, not unfrequently predominant. 

 These gases give no peculiar flavour to the water. 



b Carbonic acid renders mineral waters sparkling and effer- 

 vescent : it is detected by occasioning a precipitate in aqueous 

 solution of baryta, which dissolves with effervescence in dilute 

 muriatic acid. 



c The presence of sulphuretted hydrogen is known by its pe- 

 culiar disagreeable smell ; by the production of a black preci- 

 pitate on dropping into the water a solution of nitrate of silver ; 

 and by the deposition of sulphur on adding a few drops of 

 nitric acid. 



d The carbonates are dissolved in the water by excess of cat- 

 bonic acid, and consequently fall down upon its expulsion by 

 boiling. Carbonate of lime and magnesia are deposited in the 

 form of a white precipitate. Carbonate of iron occasions the 

 separation of a rusty brown ferruginous powder, and the water 

 is blackened by a few drops of tincture of galls. 



e Mr. R. Phillips, in his analysis of Bath waters, has shown 

 that the delicacy of galls, as a test for iron, is curiously affected 

 by the presence of certain salts : if the iron be in the state of 

 protoxide, its detection is facilitated by salts with a base of 

 lime, and by alcalis; if in the state of peroxide, lime prevents 

 the action of the test. This is well shown by dissolving a very 

 minute portion of protosulphate of iron in a glass of distilled 

 water, and adding a drop of tincture of galls, which occasions 

 no immediate discoloration ; but a drop of lime-water, or other 

 alcali, instantly renders the presence of iron evident ; so that 

 the quantity of iron present in a water cannot be correctly judged 

 of by the degree of precipitation occasioned in it by tincture 

 of galls. 



/ Ferro-prussiate of potassa is also a good test to show minute 

 quantities of iron in water, by the blue precipitate which it 

 occasions ; its action is aided by previously adding two or three 

 drops of nitric acid to the water ; but it is an equivocal test 

 compared with galls. 



