JfJtJ SPRfNttS, RIVERS, CANALS, LAKES. 



in general is of all shades, from a pale rose to the deepest black* 

 It is well known that the purple colour assumed by waters, with 

 the tincture of nut-galls, is not a proof that they contain iron in 

 its metallic state, since the sulphat and carbonat of iron likewise 

 assumes a purple colour by the infusion of nut-galls. The differ- 

 ences of colour observed in these precipitations, depend rather ou 

 the quantity of iron, its greater or less degree of adhesion 10 the 

 water, and the more or less advanced state of deposition of the 

 solution, relatively to the quantity of oxygen contained in the iron. 

 The astringent principle is known to be a peculiar acid, since il 

 unites with alkalis, converts blue vegetable colours to a red, de- 

 composes alkaline sulphures, and combines with metallic oxyds. 

 Nut-galls in powder, the infusion of this substance iu water, made 

 without heat, and the tincture by alkohol, are used 1 to ascertain 

 the presence of iron in mineral waters. The tincture is preferred, 

 because it is not subject to become mouldy as the aqueous solution 

 is. The distilled products of nut-galls likewise colour ferruginous 

 solutions. The infusions in acids, alkalis, oils, and ether, exhibit 

 the same phenomenon. The iron precipitated by this matter from 

 acids is in the state of gallat of iron, and forms a kind of neutral 

 salt, which, though very black, is not attracted by the magnet. It 

 dissolves slowly, and without sensible effervescence in acids, but 

 loses these properties by the action of tire, and is then attracted by 

 the magnet. The nut-gall is so efficacious a re-agent, that a single 

 drop of its tincture colours, in the space of five minutes, with a 

 purple tinge, three pints of water, which contains only the twenty- 

 fifth part of a grain of sulphat of iron. All these phenomena pro- 

 ceed from the great facility with which the matter of nut-galls 

 burns, and from its readily absorbing from the iron a portion of the 

 oxygen it contains, passing by this means to the state of a black 

 oxyd or ethiops, the smallest quantity of which is very perceptible 

 in transparent liquors. 



The two last reagents, we shall propose for the examination of 

 waters, are solutions of silver and of mercury in the nitric acid. 

 These have usually been employed to exhibit the presence of the 

 sulphuric, or muriatic acids in mineral waters ; but many other 

 substances, which do not contain the smallest portion of those, are 

 likewise precipitated by these solutions. The while and heavy 

 sjrise which the Bitrat of silver exhibits in water, that contains no 



