ON THE COLORS OF WATER. ?l 



evaporation. According to this, green waters, and, a fortiori, yellow 

 or brown waters, owe their color to the presence of a small quantity 

 of yellow mud. If pure water is really blue, the presence of a small 

 quantity of yellow matter would be enough to turn its color to green 

 or yellow. The same idea was advanced some time ago by M. Wilts- 

 thein, who believed he had proved, by analyses of the waters of a 

 number of Bavarian streams and lakes, that brown and yellow waters 

 contained more organic matter than green ones, and that they were 

 less hard than the latter. He thought that mineral substances of 

 themselves had no effect on the color of the water, but that organic 

 substances, naturally brown, existing in it as humic acids, were beld 

 in solution through the presence of alkaline matters with them, and 

 that they made the water, according to their abundance, green, yellow, 

 brown, or black. His views are not supported by the results of my 

 analyses, which indicated that the colors of different waters on which 

 they were made bore no relation to the quantity either of organic mat- 

 ter or of alkalies held in them. I have also not been able to find any 

 relation between the color of water and its hardness or softness. It 

 is, however, probable that very dark water may owe its color to dark 

 organic matter dissolved in it. 



M. Schleinitz attributes the diversities in the color of sea-water to 

 variations in the quantity of salt dissolved in it. During a voyage in 

 the Gazelle, from Ascension to the Congo, he observed that the blue 

 water had a higher specific gravity than that which was of a greenish 

 tinge. This observation leads to an erroneous conclusion, but affords 

 a confirmation of some results which I have reached. 



M. J. Brun has noticed in the water and the ice of the Lake of 

 Neuf chatel an alga which is green, orange, red, or brown, according to 

 the stage of growth it has reached, and black after it is dead. Its 

 presence would not be without influence on the color of the lake. 



This review shows that the problem of the color of water still calls 

 for more investigation. It may be useful to speak of a few researches 

 that I have made. My object was to determine the color of pure 

 water, and to observe the variations in color produced by the presence 

 of different substances. I used glass tubes, five metres long and four 

 centimetres in interior diameter, closed at the end with glass plates, 

 and passing through a black sheathing that intercepted the side-light. 

 They abutted against a ground-glass pane in the window of my labo- 

 ratory, so as to receive diffused light in the direction of their axes. 



M. V. Meyer, who used a similar arrangement, found the color of 

 distilled water to be a blue-green. I found it pure blue. In my first 

 experiment, I also found distilled water of a blue-green color, like that 

 of a diluted solution of ferric sulphate. A second experiment, with 

 freshly distilled water, gave a pure sky-blue, which in the course of 

 seventy hours became blue-green like the former water, without losing 

 any of its transpai*ency. This indicated that the distilled water of 



