382 



MINERAL WATERS. 



Mineral 

 Walcra. 



The acids when in combination are easily detected. 



42. Sulphuric acid is detected by the addition of ba- 

 ryta, which gives a white precipitate with any fluid con- 

 taining a sulphate. 



Other tests indicate the presence of sulphuric acid, 

 as nitrate of lead. This, however, is fallacious, as it 

 gives precipitates with other substances besides sulphu- 

 ric acid. 



In using baryta as the test of sulphuric acid, we must 

 be aware that carbonic acid likewise gives a precipi- 

 tate with baryta ; but this is easily distinguished from 

 that occasioned by sulphuric acid, the latter being inso- 

 hible, the former being soluble in muriatic and nitric 

 acids. 



Nitrate or muriate of baryta is, in general, pre- 

 ferred to the pure earth, as sulphuric acid is by them 

 more easily separated from the substance with which it 

 is in union, owing to the decomposition of the sulphate 

 being effected by double elective attraction. The most 

 powerful of the barytic salts is the muriate. Accord- 

 ing to Bergman this indicates the presence of sul- 

 phuric acid, though diluted with a million parts of 

 water. 



43. Muriatic acid is easily detected by nitrate of 

 silver, which gives a white precipitate, with water con- 

 taining a muriate. Nitrate of silver, however, gives a 

 white precipitate, when added to water containing free 

 alkali or sulphuric acid. If the former be present, it 

 must be saturated with nitric acid; if the latter exist in 

 the fluid, it must be precipitated by baryta or its nitrate. 

 The salt of silver likewise gives a white precipitate with 

 carbonic acid. This, however, is soluble in nitric acid, 

 while that occasioned by the muriatic is not. If the 

 water contain carbonic acid, previous to adding the ni- 

 trate of silver, it will be necessary to expel it by the ad- 

 dition of nitric acid and boiling. 



4i. Boracic acid is detected by means of a salt of 

 lead, with which it forms a white precipitate; but as 

 lead is precipitated by sulphuric and muriatic acids, it 

 is necessary to remove these by means of the acetates 

 of strontia and silver, having previously saturated the 

 alkalies and earths with acetic acid. 



45. The presence of an alkali, or an alkaline earth, in 

 its free state, may be known by the green colour which 

 it imparts to the vegetable blues, or by changing the 

 colour of turmeric to brown. This test, however, does 

 not point out the particular substance present. We 

 must, therefore, have recourse to other means. 



46. Polassa and soda may be distinguished from each 

 other by two different tests, muriate of platinum and 

 tartaric acid. 



When the solution of muriate of platinum is add- 

 ed to water containing potassa, a yellowish precipitate 

 falls, which is not the case when soda only is present. 



47. When tartaric acid is added to a fluid containing 

 potassa, at first there is no visible change ; but when the 

 acid is added in excess, a white precipitate is formed, 

 provided the water be not in very large quantity com- 

 pared to that of the alkali. The precipitate formed is 

 soluble in nitric and muriatic acids ; but tartaric acid, 

 when added to a fluid containing soda, does not occa- 

 sion any perceptible change. 



In using tartaric acid as a test of potassa, the fluid 

 must be concentrated by evaporation, otherwise the su- 

 pertartrate of potassa is not deposited, being soluble in 

 a large quantity of water. These tests also distinguish 

 potassa from soda, when they are in combination with 

 an acid. 



48. Lime, in union with carbonic acid, is easily de- 

 tected by boiling the fluid, by which means the super- 

 abundant carbonic acid is driven off, and the carbonate 

 of lime is deposited, the precipitate being soluble in ni- 

 tric and muriatic acids, and also by the addition of wa- 

 ter containing carbonic acid. Lime, however, frequent- 

 ly exists combined with a fixed acid. When this is the 

 case, no change takes place on boiling the fluid. The 

 most delicate test of the presence of lime, when in this 

 state, is oxalic acid. This, when added to water con- 

 taining a salt of lime, gives a white precipitate, which 

 is soluble in nitric and muriatic acids. In using oxalic 

 acid as a test of lime, we may employ either the acid 

 pure, or in combination with ammonia. The latter, 

 though not the most delicate, is the best, as the alkali 

 combines with the acid with which the lime is in union, 

 and prevents it from acting on the precipitate. If any 

 free acid be present in the water, it must be neutralised 

 by ammonia, and, if we have reason to suspect the pre- 

 sence of baryta, it must be precipitated by sulphuric 

 acid. Oxalic acid, it must be remarked, likewise occa. 

 sions a precipitate with magnesia ; but the precipitation 

 of this earth does not take place for many hours, while 

 that with lime occurs the moment that the oxalate is 

 added. 



49. Baryta may be detected by the addition of sul- 

 phuric acid, with which it gives awhile precipitate, not 

 soluble in nitric or muriatic acid. Previous to the ad- 

 dition of the acid, it is necessary to remove the lime, as 

 it may, if present in considerable quantity, also occasion 

 a white precipitate with it. 



50. Magnesia is precipitated by the alkalies and by 

 lime. These tests, however, are liable to fallacy. Thus 

 if carbonic acid be present, and we employ lime as 

 the test, carbonate of lime will be precipitated. If 

 the water contain sulphuric acid, sulphate of lime may 

 likewise be formed and deposited. When ammonia is 

 used as the test of magnesia, if carbonic acid be present, 

 carbonate of ammonia will be generated, which, if the 

 water contain a salt of lime, will be decomposed, and 

 carbonate of lime will be precipitated. In detecting 

 magnesia, then, if we suspect the presence of the other 

 substances mentioned, nitric acid must be added to 

 decompose any carbonate, and the fluid boiled. The 

 sulphuric acid must then be precipitated by bary- 

 ta. 



The alkalies and lime-water also precipitate alumina : 

 this is another source of error, in using those bodies as 

 a test of magnesia. Alumina, however, rarely occurs 

 in mineral waters ; if it does, and is precipitated along 

 with the magnesia, it is easily separated from that earth. 

 For this purpose, after washing the precipitate, it must 

 be boiled in a solution of potassa, by which the alumina 

 is dissolved, and the magnesia is left. Or, the precipitate 

 may be dissolved in strong muriatic acid, and an alka- 

 line carbonate added to the solution ; the precipitate 

 which is thrown down by this must be washed and 

 dried at the temperature of about 100. Diluted mu- 

 riatic acid is then to be poured on it, which will dis- 

 solve the magnesia, but will not act on the alumi- 



na. 



51. Alumina is detected by the methods just describ- 

 ed for discovering the presence of magnesia. Suc- 

 cinic acid, or its compound with ammonia, is another 

 test of alumina, as it precipitates this earth, but does 

 not affect magnesia ; the former methods are, however, 

 generally employed. 



52. Silica may be discovered by evaporating the 



