TRANSACTIONS OP THE SECTIONS. 83 



On the Supply and Purification of Water. 

 By Thomas Spencer, F.C.S. 



The author stated that, from an extensive practice in relation to the chemistry of 

 water for the supply of towns, he became convinced that the available quantity of 

 pure water in these islands was gradually decreasing, whilst it was evident the demand 

 for this primary necessary of life was undergoing an almost corresponding increase ; 

 in short, that in the more cultivated districts the supply was every year becoming 

 less capable of meeting the demand. 



After pointing out various facts bearing on this result, the author proceeded to 

 consider the purification of water. 



The opinions of the best authorities With regard to the probability of effecting the 

 purification of water by any artificial means, were summed up at the conclusion of 

 the report drawn up by the Government Commissioners, " On the Supply of Water 

 to the Metropolis." These gentlemen there said that " whatever substances may be 

 employed in filtering beds, water cannot be deprived of matter held in solution by any 

 practical modification of the process of filtration." This was the state of the subject 

 when entered on by him. His object, from the beginning, was to discover the mode 

 by which nature converted impure coloured surface water into colourless spring water, 

 the operation being apparently one analogous to filtration. His first experiments 

 were made with a view of throwing some light on the philosophy of filtration itself as 

 ordinarily practised, having some reason to believe that the process, when most 

 effective, did not so much depend on mechanical principles as was generally supposed. 

 To determine this point, a series of experiments was related to the Section. They 

 resulted in showing that properly conducted filtration (i. e. where the gravitating 

 power of the water is not in excess) depends on a lateral attractive action exercised 

 by the sand or other medium through which the process is performed, in addition to 

 the downward action of gravitation. His next object was to discover what bodies in 

 nature exercised this attractive power the best. After trying a number of experiments 

 with various descriptions of rocks and minerals, all of which were described to the 

 Section, he found that those containing protoxide of iron (even where it was chemi- 

 cally combined with other substances) effected the filtration of water from even 

 suspended impurity better than any others. Acting on the idea thus suggested, he 

 found that the same oxide, when isolated in the state of " magnetic oxide," not only 

 freed water from turbidity more effectually than an equal thickness of sand, but 

 effected its decoloration with marvellous rapidity. On the other hand, the earthy 

 substances entering into the composition of the same rocks, such as silica and alumina, 

 when isolated, were, in the latter respect, perfectly inert. From this it was evident 

 that the protoxide of iron, as magnetic oxide — a substance which enters into the 

 composition of so many rocks — was one of nature's chief agents of purification. Here 

 the author referred to a series of experiments he had previously made, which resulted 

 in showing that the commonly received opinion, that light and air alone effected the 

 purification of water, was partially erroneous. For example, he had put coloured 

 bog water into shallow glass pans, in which it was fully exposed to both these agencies 

 for several weeks — evaporation being compensated by distilled water — but without 

 any change becoming apparent in its colour. This result, so contrary to what he 

 was led to expect a priori, induced him, at the time, to refer the natural oxidizing 

 process to the agency of some other body which probably exercised a catalytic action 

 on atmospheric oxygen, and thereby induced this gas to combine with the noxious 

 impurities it met with in the water. Nor was he mistaken in this surmise, as the 

 results so amply related in the paper, together with the experiments exhibited to the 

 Section, sufficiently proved. A most striking experiment was made with some bog 

 water, darker in colour than ordinary porter, which had been procured from the 

 soakings of an Aberdeenshire peat bed. When brought into contact with the oxide, it 

 was deprived of its colour almost instantaneously, and carbonic acid substituted in its 

 place. 



To appreciate this result, it is to be remembjred that no known agency had been 

 able to effect a similar one before. The excess of carbonic acid found in spring water 

 has hitherto never been understood, though henceforth it will be easily accounted 

 for. Since soft water had become so much an object for manufacturing purposes, to 

 effect the decoloration of that of bogs had remained a practical problem, the solution 



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