BLUE WATER 81 



process " in use ; and the splendid blue colour of the water 

 in the " softening " tanks at Plumstead, when the process 

 was first used by the North Kent Water Company, sixty- 

 four years ago. 



It is, I think, still a possible question as to whether the 

 fine floating particles of precipitating chalk act in any way 

 as a " cloud " — in short, as the blue clouds of smoke, egg- 

 white, milk, and varnish. There is no evidence that they 

 do, but no one, so far as I know, has ever taken the trouble 

 to settle the question. It could be done by examining the 

 blue light from the tanks with a polariscope, and also by 

 sinking a black tarpaulin into the tank to cover the white 

 floor and hanging others at the sides. Then if the blue 

 colour were due to light reflected from the white floor and 

 sides traversing repeatedly the clear self-coloured blue 

 water, the blue colour should no longer be visible, for the 

 reflecting surfaces would be covered by the black tarpaulin 

 and little light sent up through the water. But if it were 

 due to a cloud of greatest delicacy in the water — like fine 

 smoke reflecting the blue light rather than the other rays 

 — then the colour should be as intense or more intense 

 when the black background is introduced. I am surprised 

 that some inquirer, younger and more active than I am, 

 does not put the matter to the test of experiment. 



On the whole, practically all the facts which we know 

 about " blue water " are consistent with the blue self-colour 

 of water, and not with that of a " blue cloud " in the water. 

 Now that we have porcelain baths of the purest white and 

 of large size, one may often see the strong blue colour of 

 water of great purity in the bath, especially where waves 

 or ripples send to our eyes those rays of light which have 

 taken a more or less horizontal course from side to side of 

 the bath, and have thus been through a large thickness of 

 the pale-coloured fluid. Great masses of clear ice, such as 

 one may study in glaciers, are blue ; the " crevasses " which 

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