PHYSICAL EXPERIMENTS. 47 



three or four inches high. Let the bottle be about half 

 filled with this solution. Into a few drops of bisul- 

 phide of carbon drop a piece of iodine. It will at once 

 stain the bisulphide a dark-brown color, which should 

 then be carefully dropped upon the solution of zinc, 

 where it will float. If now pure water be carefully 

 added, so as to rest upon the solution of zinc, the bi- 

 sulphide will collect into an oblate spheroid, having the 

 appearance of brown-colored glass. A square bottle 

 will enable one to project it better, as a round bottle 

 would make a cylindrical lens, and the projection would 

 be indistinct, unless the vessel was quite large. 



Nearly fill the large tank (Fig. 20) with alcohol, and 

 project the tank with the lantern, or with the single 

 lens and porte litmiere. Now drop upon the alcohol, 

 with a glass rod, or other convenient thing, any of the 

 aniline dyes. As soon as the dye touches the alcohol 

 it will go straight down for a short distance, then it will 

 branch, and these will shortly branch again, and so on 

 to the bottom of the tank, when there will be a large 

 number of branches. Upon the screen the appearance 

 will be as if a tree were growing ; if at short distances 

 apart in the tank drops of different colors are placed, 

 the branches will interlace and produce a fine effect. A 

 tank of coal-oil, in which is dropped a little colored 

 fusil oil, is said to produce an entirely different figure. 



But it is with the vertical attachment that the most 

 novel and interesting phenomena, due to cohesion, may 

 be shown. For this purpose it is necessary to have a 

 horizontal tank, made by cementing a ring, an inch 

 broad and four or five inches in diameter, upon a plate 

 of clear glass. The ring may be made of glass, or 

 wood, or zinc. This is to be placed upon the hori- 

 zontal condenser, and half filled with pure water, the 



