SCIENTIFIC NEV\^S. 



[Aug. 1st, 1887. 



that of venous blood have thrown light on several important 

 physiological problems. For example, certain peculiar bands 

 are present when the blood contains a minute quantity of car- 

 bonic oxide, and thus poisoning by charcoal fumes can be 

 readily detected. One thousandth part of a grain of blood 

 is sufficient to reveal the characteristic spectrum to a prac- 

 tised eye. 



Mr. Sorby, who has given much attention to this subject, 

 has found that the year of vintage of a sample of wine can 

 be determined within one year during the first six years, 

 but that after this the changes are less striking. He took 

 specimens of various ports from the casks, of different ages 

 up to six or seven years, and labelled them in such a manner 

 that he did not know the age of any, but could ascertain it 

 afterwards by reference. He then made the observation 

 with a spectroscope with great care, and found that by 

 proper attention to the bands and their positions he could 

 correctly determine the year of vintage of each particular 

 specimen. It is said that raw fiery whiskey subjected 

 to the passage of a current of electricity is much improved 

 by the electrolytic oxidation of the oils and other offensive 

 constituents; it would be interesting to try whether the 

 same means would age wine in a manner that would deceive 

 both palate and spectroscope. 



THE COLOUR OF WATER. 



IT is well known that water is often coloured by the 

 ingredients which it holds in suspension, but when all 

 organic and inorganic matter has been removed, what 

 then is the inherent colour of water ? Or is it colourless ? 

 An idea was once prevalent that the water of a sea or 

 lake was blue, by reason of the reflected blue of the sky 

 above, and no doubt the reflected light of the sky has a 

 most important influence on the apparent colour of the 

 water. If the sky be deep blue, then this blue light, when 

 reflected by the surface of the water, causes it to appear of 

 a deeper and richer blue. Only fifteen years ago Sir 

 Robert Christison was thought to have proved satisfactorily 

 by experiments that, without the impurities suspended in 

 it, water had no colour. In dry weather the waterfalls 

 presented the purest whiteness, and water from many 

 gravel beds seemed to be brilliantly transparent. It was, 

 then, a natural and excusable delusion on his part to con- 

 sider that water had no colour. But other scientific men 

 had doubts about this. They were haunted by the 

 idea that water had colour, and they could not account 

 for certain results on the no-colour theory. Sir John 

 Herschel was of opinion that the explanation of many 

 colour phenomena had yet to be found, unless the 

 simple but somewhat doubtful hypothesis were granted, 

 that water had a selective power of absorbing colour. Dr. 

 Tyndall next showed by experiment that water had a 

 decided colour. He passed the light from an electric lamp 

 through distilled water in a tube fifteen feet long, and he 

 cast a magnified image of the end of the tube on a screen. 

 In this way he showed that the colour of the water was 

 blue-green. Since then Mr. John Aitken has entered upon 

 a series of experiments, the results of which we are now 

 able to give. 



In the first set of experiments he let down into the 

 water, close to a white object, a long metal tube open at 

 one end and closed at the other by a clear glass plate. The 

 object appeared of a most beautiful deep and delicate 

 blue at the depth of twenty feet. This he could not 

 account for by the selective reflection theory, which holds 

 that the colour of the object is due to the light reflected by 

 infinitesimally small particles of matter suspended in the 

 water, because in that case the object would have been 



illuminated with the complementary colour yellow. He, 

 therefore, adopted the theory that the colour of the water 

 was due to the selective absorption of the water. In the 

 second set of experiments, a very long blackened tube 

 (which had a clear glass plate attached to the lower end), 

 was filled with the purest natural water, and through this 

 a white disc was examined. The light transmitted was 

 found to be blue, because the water absorbed the rays at 

 the red end of the spectrum. In the third set of experi- 

 ments, objects of different colour were sunk into the water, 

 and these colours were found to change and appear as it 

 they were looked at through a piece of pale-blue glass. A 

 white object appeared blue ; a red object darkened as it 

 descended, and soon lost its colour ; very brilliant red 

 appeared dark brick-red at the depth of seven feet ; a 

 yellow object changed to green, and a purple object ap- 

 peared deep blue, All these changes indicated an absorp- 

 tion of the red components of the colours. When again, 

 the coloured objects were sunk in water specially prepared 

 and coloured blue by reflection from small particles, the 

 white changed to yellow, the yellow simply deepened in 

 colour, and the purple grew redder. On these experiments 

 was based the hypothesis that water is a blue transparent 

 medium, acting in the same way as a solution of a blue 

 salt, or as a blue-coloured glass. 



The concluding test was with distilled water, the purest 

 water obtainable being boiled, and the steam being col- 

 lected and condensed by a slow process, the distilled water 

 being then used for the experiments. The test was also 

 varied by distilling three different samples of clear water 

 in three different sets of apparatus ; one was made of glass, 

 one of brass, and one had a platinum condenser. Mr. 

 Aitken supposed that if the colour was due to impurities, 

 the impurities in the three samples would be different, 

 and that the colours would be different also. When 

 the darkened tubes used in the second set of ex- 

 periments were filled with these distilled waters, and a 

 white surface was looked at through them, the effect in all was 

 the same — the colour was blue, almost exactly of the same tint 

 as a solution of Prussian blue. Assuming, as we do, that 

 the water in no case was chemically pure or absolutely free 

 from suspended particles, we are of opinion that little or no 

 difference would be produced by distilling the water in ap- 

 paratus made of different materials. Apart from this con- 

 sideration, however, the broad fact remains that perfectly 

 clear water when distilled gave a characteristic colour. 



Another fact of importance must also be noticed. Though 

 the selective absorption of the water determines its 

 blueness, its brilliancy depends on the solid particles sus- 

 pended in it. A piece of blue glass, or a blue solution, has 

 little colour when looked at from the side on which the 

 light is falling ; and light will permeate clear water till it is 

 all absorbed. The brilliancy of some waters must there- 

 fore be due to something in suspension. If samples of 

 the water of the Mediterranean taken at different places be 

 examined by a concentrated beam of light, millions of dust 

 particles of different kinds and sizes are detected floating 

 through the water. The solid particles are white, but are 

 more numerous in some places than in others. Little light 

 is reflected when these particles are few, and the colour is 

 then deep blue. But when the particles are more nume- 

 rous there is an increased reflection of light, and the colour 

 is blue-green. The colour is deep blue in the former case 

 because the light penetrates to a greater depth and becomes 

 more highly coloured than when the particles are more 

 numerous, and the light is prevented from penetrating far. 

 Along the shores of the Mediterranean the water washes 

 the rocks and rubs off the fine particles which make it so 

 beautifully brilliant. At one place, where the limestone is 



