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



duction of nitrous acid by the action of iron upon the nitrogenous 

 compounds contained in the water. 



The brown deposit from a gallon of Thames water was col- 

 lected in a porcelain capsule, di'ied at 248° P. and weighed. It 

 amounted to 4*4352 grs., and consisted of — 



10008 



A second deposit produced by iron in four gallons of water 

 was collected in a similar manner, and dried in an air-bath at 

 248° F. It weighed 142450 grs., and lost on ignition 24-31 

 per cent, of volatile matter. 



To ascertain the actual effect produced by iron, I made a series 

 of determinations of the solid residue and organic matter con- 

 tained in Thames water before and after being placed in contact 

 with iron. Four separate determinations of solid residue and 

 organic matter in the water which had not been in contact with 

 iron, were made on four consecutive days in January last with 

 the following results : — 



Solid residue from Organic matter 

 one gallon. in the residues, 



grs. grs. 



1 20-867 2-248 



II 19-573 1-740 



III 21-159 1-424 



IV 20-127 1-401 



Average . . . 20-4315 1-7032 



Having found that iron promotes the precipitation of organic 

 matter from Thames water, it appeared desirable to ascertain the 

 quantity of iron and the length of time necessary to effect the 

 entire destruction or precipitation of the organic impurities con- 

 tained in it. To accomplish this I instituted the following ex- 

 periments : — 



1st. In a gallon of water was immersed one coil of fine iron 

 wire weighing half an ounce. It was allowed to stand two 

 hours, and the water then filtered ; when filtered and evaporated 

 and the residue dried in an air-bath at 248°, till it ceased to 

 lose weight, it gave, — 



Solid residue 17-3712 grs. 



Including matter volatile on ignition. 1-2320 „ 



