Professor Bunsen on the Colour of Water. 95 



have taken place, according to some authors, in the tertiary 

 epoch 1 This is a point we cannot now decide. However 

 this may be, it is not less true that the eruptions which have 

 furnished the materials of the Taviglianaz sandstones, may 

 have been accompanied with disengagements of sulphurous 

 acid and hydrochloi-ic acid, and exercised an influence on the 

 formation of the dolomites of Savoy analogous to that which 

 the pyroxenic eruptions of the Tyrol have exerted on the ori- 

 gin of the dolomite of that countrv. 



On the Colour of Water. By Professor BuNSEJf. 



The hot springs which occur in many pai'ts of Iceland, and 

 are especially remarkable at Reykir, are, says that excellent 

 observer Bunsen, characterised by extreme beauty. In the 

 depths of the clear unruffled blue waters of these basins, from 

 which rises a light vapour, the dark outlines of what once 

 formed the mouth of a Geyser may be faintly traced amid the 

 fantastic forms of the white stalactic walls. Nowhere can 

 the beautiful greenish-blue tint of water be seen in greater 

 purity than in these springs. 



A few remarks on the causes from which they are derived 

 will hardly be superfluous. 



Chemically-pure water is not colourless, as is usually sup- 

 posed, but naturally possesses a pure bluish tint, which is only 

 rendered visible to the eye when tlie light penetrates through 

 a stratum of water of considerable depth. That such is the 

 fact, may easily be shewn by taking a glass tube, two inches 

 wide and two yards long, which has been blackened internally 

 with lamp-black and wax to within half an inch of the end, 

 the latter being (jlosed by a cork. Throw a few pieces of 

 white porcelain into this tube, wliich, after being filled with 

 chemically-pure water, must be set vertically on a white 

 plate, and looking through the column of water (of two yards) 

 at the pieces of porcelain, which can only be illumined from 

 below by white light, we shall observe that the objects will, 

 under the.se circumstances, acquire a pure blue tint, the in- 



