170 FRAGMENTS OF SCIENCE. 



kindness of Professor Frankland, I have been furnished 

 with specimens of the water of eight London companies. 

 They are all laden with impurities mechanically sus- 

 pended. But you will ask whether filtering will not 

 remove the suspended matter? The grosser matter, 

 undoubtedly, but not the more finely divided matter. 

 Water may be passed any number of times through 

 bibulous paper, it will continue laden with fine matter. 

 Water passed through Lipscomb's charcoal filter, or 

 through the filters of the Silicated Carbon Company, 

 has its grosser matter removed, but it is thick with fine 

 matter. Nine-tenths of the light scattered by these 

 suspended particles is perfectly polarised in a direction 

 at right angles to the beam, and this release of the 

 particles from the ordinary law of polarisation is a 

 demonstration of their smallness. I should say by far 

 the greater number of the particles concerned in this 

 scattering are wholly beyond the range of the micro- 

 scope, and no ordinary filter can intercept such particles. 

 It is next to impossible, by artificial means, to produce 

 a pure water. Mr. Hartley, for example, some time 

 ago distilled water while surrounded by hydrogen, but 

 the water was not free from floating matter. It is so 

 hard to be clean in the midst of dirt. In water from 

 the Lake of Geneva, which has remained long without 

 being stirred, we have an approach to the pure liquid. 

 I have a bottle of it here, which was carefully filled for 

 me by my distinguished friend Soret. The track of the 

 beam through it is of a delicate sky-blue ; there is 

 scarcely a trace of grosser matter. 



The purest water that I have seen probably the 

 purest which has been seen hitherto has been obtained 

 from the fusion of selected specimens of ice. But extra- 

 ordinary precautions are required to obtain this degree 

 of purity. The following apparatus has been con- 



