and the Cunstituents of Well- and River-ivaters. 59 



and allowed to remain for two hours. As in former experi- 

 ments, the white cloud made its appearance. At the end of two 

 hours, the water was filtered through fine white sand (paper 

 allowing the precipitate to pass through) till it became perfectly 

 bright. These three gallons were afterwards evaporated in a 

 manner similar to the preceding, and gave not the slightest in- 

 dications of sulphuretted hydrogen or a volatile sulphuret. 



To each of several Winchester quarts of distilled water, was 

 added a cubic centimetre of strong hydrosulphuret of sulphide 

 of ammonium. Several coils of iron wire, weighing two ounces, 

 were put into each bottle and allowed to remain. In a few 

 minutes a white cloudy preci])itate formed ; at the end of 

 twelve hours the water was filtered through fine sand, and in 

 the clear filtrate no indications of the sulphide could be obtained, 

 the sulphide of anmionium having been entirely decomposed by 

 contact with iron. 



By the kindness of Mr. Quick, engineer of the Southwark 

 and Vauxhall and Grand Junction Water Companies, I have 

 had an opportunity of trying the action of iron upon Thames 

 water on a much larger scale than is possible in a laboratory. 

 A brick and cement tank was constructed capable of holding 

 1600 gallons. In this was suspended, by means of cross-bars, 

 twelve pounds of iron wire. In an hour, the water, previously 

 very bright, became opake and muddy, and in twenty-four 

 hours there was a dark-coloured flocculent precipitate, consist- 

 ing of organic mattci', oxide of iron, silica, and the carbonates 

 of lime and magnesia. The water was now filtered through 

 three feet of the usual filtering medium (coarse and fine sand). 

 It came through perfectly bright and colourless. Eight gallons 

 of this water were reserved for analysis, and at the same time 

 eight gallons of the filtered water from the stand-pipe were 

 taken for comparison. An analysis of each was made under 

 precisely similar circumstances, with the following results. It 

 may be observed, that the residues were dried for the same 

 length of time, and at the same temperature (248° F.). 



No I. is the water from the works filtered through sand, and 

 as su|)|)lied to the mains. 



No. II. The same water, before filtration, in contact with iron 

 for twenty-four hours (twelve jjounds of iron wire to 1600 

 gallons of water). 



