40 Mr. West on Natural Waters. 



diminution, and not much impairing the transparency or re- 

 fractive power of the water. It is quickly and completely 

 separated by aluminous earth in a state of minute division; 

 the alumine, at first snow-white, becoming brown, and forming 

 a true lake. It is separated by muriate of tin, in flakes com- 

 posed of colouring matter and oxide of tin. Many other of its 

 habitudes agree all, indeed, which I have compared. Thus 

 it more readily leaves the water> and fixes itself on the material 

 boiled or washed in it, when that is of silk or woollen, animal 

 productions than when linen or cotton, vegetable fabrics. 

 Printed cotton, however, of bright colours, is at once stained 

 and altered, from the mordant of the print combining with or 

 fixing the additional colour. White linen or calico, on the 

 other hand, once washed in pale yellow water, is not percep- 

 tibly stained ; with deep brown water it is discoloured by the 

 first operation ; and the same result takes place from the re- 

 peated use of that which, in a single trial, produces no sensible 

 effect. 



Though this substance obstinately resists mere filtering, such 

 as would separate suspended impurities, yet sand, containing, 

 as I apprehend, some alumine, is effectual in separating it: 

 but the kind of sand which will filter at once most speedily 

 and effectually ; the degree of mixture with clay which will 

 produce the greatest chemical effect without lessening mate- 

 rially the permeability of the sand ; the depth of sand required ; 

 the fall or pressure which best unites speed and effect; all 

 these are points calling for experiment, and which, if not well 

 ascertained before attempting to filter on the great scale, may 

 cause much useless delay and expenditure. Long exposure in 

 reservoirs to light and air, assisted, as I believe, by the action 

 of the clay with which they are lined, destroys the colour. 

 The water with which one large town is supplied enters the 

 reservoirs more deeply stained than any of the streams which 

 formed the subject of my experiments ; and left them, at the 

 time it was brought to me, less coloured than the water of the 

 river Aire. But I am told that, in winter time, when a flood 

 happens, the water from the surface, leaving each reservoir 

 soon after it enters, is delivered from the pipes to the houses 



