418 PROFESSOR CONNELL ON THE PRESENCE OF ORGANIC MATTER 



the circumstances that nitrate of silver seldom shews an equal, and generally a 

 much less, degree of muddiness, and that that reagent, in no case of such waters 

 which I have tried, ever produces a dense, curdy precipitate, establish that the 

 effect is not due to any muriate ; for a solution containing such a constituent, 

 and giving even a curdy precipitate with nitrate of silver, may, nevertheless, be 

 too weak to be affected by acetate of lead. The most probable view, therefore, 

 which occurred was, that the reaction is due to the presence of organic matter ; 

 and this became the more likely, when it was observed that rain-water is scarce- 

 ly affected by acetate of lead, although some of the other reagents are not with- 

 out action on it.* Of course, as already stated, where the water contains a suf- 

 ficient quantity of inorganic salts to produce their proper reactions with the lead 

 solution, the above appearances will be modified accordingly. 



I made several attempts to insulate the matter in combination with oxide of 

 lead, by subjecting the precipitate to the action of sulphuretted hydrogen. The 

 water employed for this purpose was the town water of St Andrews, which pro- 

 ceeds from springs in the rising ground to the south side of the town, and is con- 

 veyed into the houses in pipes. In its ordinary state it is transparent and colour- 

 less. It contains from 7^00 * Woo f solid inorganic constituents, which are 

 sulphate of magnesia, carbonate, sulphate, and muriate of lime, with a trace of 

 muriate of potash. When fresh drawn from the pipes, it deposits a very little 

 ochreous matter ; and, on the whole, if it may not be ranked amongst the purest 

 of spring waters, it at least is of greater purity than the ordinary colourless water 

 of wells and running streams. This St Andrews water gives a pretty copious 

 white precipitate with acetate of lead, which is easily dissolved by a drop or two 

 of nitric or acetic acid, without visible effervescence ; and previous boiling scarcely 

 diminishes the amount of this precipitate. It is equally formed if the lead-salt 

 is added to the water after the latter has been allowed to stand some weeks 

 in a glass jar, so as to separate every thing which is capable of subsidence. 

 If, after adding the acetate of lead, the water is allowed to remain at rest 

 for about a quarter of an hour, a farther precipitation then begins, which is 

 no longer soluble in weak acids, and which is now sulphate of lead. Barytic 

 salts immediately indicate the presence of sulphates, but the muddiness is 



* It will be found, that if the solution of acetate of lead is prepared by dissolving sugar of lead in 

 any well or spring water, which gives a considerable cloud with that salt, and is then filtered, it is less 

 readily affected by carbonic acid in any liquid to which.it may be added, than when it has been prepared by 

 solution in distilled water. Itwas a solution of the former kind that was employed in the above experiments. 

 Of all tests for free carbonic acid in solution, the most delicate is a solution of basic acetate of lead. It 

 instantly indicates traces of carbonic acid in distilled water, on which lime-water has no action, and ba- 

 rytic water a comparatively feeble one. It seems to be for carbonic acid in solution what silver salts are 

 for muriatic acid, or barytic salts for sulphuric. 



