320 FRAGMENTS OF SCIENCE. 



pended in it. But when we remember that this perfection 

 of blue is ajiproached gradually through stages of less per- 

 fect blue; and when we consider that a blue in all re- 

 spects similar is demonstrably obtainable from particles 

 mechanically suspended, we should hesitate, I think, to 

 conclude that we have arrived here at the last stage of pu- 

 riBcation. The evidence, I think, points distinctly to the 

 conclusion that, could we push the process of purification 

 still further, even this last delicate trace of blue would dis- 

 appear. 



Chalk - "Water. Clark'' s Softening Process. 



But is it not possible to match the water of the Lake 

 of Geneva here in England ? Undoubtedly it is. We have 

 in England a kind of rock which constitutes at once an ex- 

 ceedingly clean recipient and a natural filter, and from which 

 we can obtain water extremely free from mechanical im- 

 purities. I refer to the chalk-formation, in which large 

 quantities of water are held in store. Our chalk-hills are 

 in most cases covered with thin layers of soil, and with 

 very scanty vegetation. Neither opposes much obstacle 

 the entry of the rain into the chalk, where any organic 

 impurity which the water may carry in is soon oxidized 

 and rendered harmless. Those who have scampered like 

 myself over the downs of Hants and Wilts will remember 

 the scarcity of water in these regions. In fact, the rain- 

 fall, instead of washing the surface and collecting in streams, 

 sinks into the fissured chalk and percolates through it, and 

 when this formation is suitably tapped we obtain water of 

 exceeding briskness and purity. Here is a large globe filled 

 with the water of a well near Tring. It is wonderfully free 

 from mechanical impurity ; indeed, it stands to reason that 

 water wholly withdrawn from surface contamination and 

 percolating through so clean a substance should be pure. 

 Sending a beam through this glass of water its purity is 



