52 Mr. H. Medlock on the Reciprocal Action of Metals 



The water had the peculiar fish-like smell of the masses of 

 " flab " [Ulva intestinalis) floating on the surface. The stones on 

 the sides of the canals, the hurdles placed to keep up the sand, 

 floating pieces of stick, and indeed every solid body with which 

 the water came in contact, was coated with a reddish- brown de- 

 posit similar to that which was found to separate from the filtered 

 water in Amsterdam. This deposit was particularhj abundant 

 near the iron sluice-gates. A pipe from one of the mains in 

 Amsterdam was examined at the same time, and found to be 

 coated on the inside with a thick slimy deposit of vegetable 

 remains, which presented under the microscope an appearance 

 similar to that of the deposits above alluded to. 



Remembering the important fact established by Schonbein, 

 that copper and platinum in a finely-divided state have the pro- 

 perty of converting ammonia into nitrous acid, and having myself 

 demonstrated that lead, in any form*, possesses a similar power, 

 it occurred to me that if the same property were possessed by 

 iron, it would throw a light upon the fact of the separation of 

 organic matters from waters which remain in contact with that 

 metal. Schonbein states that finely-divided copper and platinum 

 convert ammonia instantaneously, at the common temperature, 

 into nitrous acid, while " iron requires to be heated to a dull 

 redness " before it will effect a similar change. 1 have found, 

 however, that on placing several coils of iron wire in a bottle 

 and adding a few drops of strong ammonia, a slight elevation of 

 temperature takes place, and after an hour nitrous acid may be 

 detected by the acidulated starch-paste and iodide of potassium 

 test. T tried also the action of iron which had been reduced 

 from the oxide by hydrogen, and found that it instantly converted 

 a portion of the ammonia into nitrous acid. 



In order to study the action of iron upon the Amsterdam 

 water, I submitted to analysis a quantity of this water which 

 had never been in contact with iron, and at the same time I im- 

 mersed several coils of iron wire in two gallons of the same water. 

 The water in which the iron wire was placed was perfectly bright 

 and free from colour, and had nothing visible in mechanical 

 suspension except a few of the siliceous tubes above alluded to. 

 The experiment was made in four open glass bottles. 



A series of remarkable phaenomena wei'e observed. In five 

 minutes a faint white cloud was seen radiating from the coil of 

 iron wire and descending in the form of a pai-achute. In half 

 an hour the cloud increased in density, and the water became 

 opalescent. In six hours the cloud assumed a brownish colour, 

 and there was a brown deposit at the bottom of each of the 



* Learl pjTopliorus dropped into a. bottle containing the vapour of am- 

 monia mixed with air, instantly ])roduces nitrite of ammonia. 



