and the Constituents of Well- and River-waters. 



53 



bottles. The cloud continuing to increase during forty-eight 

 hourSj assumed more and more a flocculent character and a 

 reddish coloui', exactly like the deposit from the Amsterdam 

 water which had flowed through iron pipes. The water was now 

 filtered through fine Swedish filter-paper, submitted to analysis, 

 and a portion of the deposit examined under the mici'oscope. 

 The latter consisted of the remains of algae, each separate flock 

 having a siliceous tube as a nucleus. The remainder of the de- 

 posit was burned, and the ash found to consist of iron-oxide, 

 silica, and the carbonates of lime and magnesia. 



The following are the analyses of the water before and after 

 bein^ in contact with iron : — 



Water from the 

 Duin canals 



Sulphate of lime .... 3*70 



Chloride of sodium . . . 4' 10 



Carbonate of lime .... 5-60 



Carbonate of magnesia . . 3'97 



Silica 0-16 



Iron, alumina and phosphates. 0*95 



Matter volatile on ignition . 2-10 



20-58 



II. 



The same water which 



had been in contact with 



iron for forty-eight hours. 



3'68 grs. per gal. 



4-01 „ 



3-20 



1-30 „ 



trace 



trace 



trace 



1219 



By these analyses, it is seen that the 2*10 grs. of organic 

 matter originally contained in the water ivas decomposed or 

 thrown down by contact ivith iron. The water thus purified no 

 longer possessed the unpleasant fish-like taste and odour which 

 had marked its previous contamination. 



A portion of the water which had been in contact with iron 

 wire was rendered slightly alkaline by pure alcoholic potassa, 

 evaporated to dryness, and the residue tested for nitrous acid. 

 The paper became instantly blue. In the residue of the water 

 which had not been in contact with iron, and still containing its 

 organic matter, no indications of nitrous acid could be obtained. 

 Thus it appears that iron possesses the property of jjroducing 

 nitrous acid from the nitrogen of organic matter, or from the 

 ammonia existing in the water. This nitrous acid, as appears 

 from experiments subsequently to be detailed, seems to act the 

 part of a scaveiujer in the water, oxidizing every ])article of pu- 

 trescent or putrescible matter which may be contained therein. 



The water of the Thames, and indeed that of nearly all other 

 rivers, contains a large quantity of decaying organic matter 

 derived from the plants and animals abounding in the streams. 



