146 FRAGMENTS OF SCIENCE 



ins in alcohol. Dropped into water, the scented Jdquid 

 immediately produces a white cloudiness, due to the pre- 

 cipitation of the substances previously held in solution. 

 The solid particles are, however, comparatively gross ; but, 

 by diminishing the quantity of the dissolved gum, the pre- 

 cipitate may be made to consist of extremely minute parti- 

 cles. Briicke, for example, dissolved gum-mastic, in cer- 

 tain proportions, in alcohol, and carefully dropping his 

 solution into a beaker of water, kept briskly stirred, he 

 was able to reduce the precipitate to an extremely fine 

 state of division. The particles of mastic can by no means 

 be imagined as forming bladders. Still, against a dark 

 ground — ^black velvet, for example — the water that con- 

 tains them shows a distinctly blue color. The bluish color 

 of many liquids is produced in a similar manner. Thin 

 milk is an example. Blue eyes are also said to be simply 

 turbid media. The rocks over which glaciers pass are 

 finely ground and pulverized by the ice, or the stony 

 emery imbedded in it; and the river which issues from 

 the snout of every glacier is laden with suspended matter. 

 When such glacier water is placed in a tall glass jar, and 

 the heavier particles are permitted to subside, the liquid 

 column, when viewed against a dark background, has a 

 decidedly bluish tinge. The exceptional blueness of the 

 ijake of Geneva, which is fed with glacier water, may be 

 due, in part, to particles small enough to remain suspended 

 long after their larger and heavier companions have sunk 

 to the bottom of the lake. 



We need not, however, resort to water for the produc- 

 tion of the color. We can liberate, in air, particles of a 

 size capable of producing a blue as deep and pure as the 

 azure of the firmament. In fact, artificial skies may be 



