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APPARATUS FOR ILLUSTRATING BoyLE’s Law. 
By F. M. ANDREWS. 
The apparatus shown in Figure 1 illustrates not only Boyle’s or Mari- 
otte’s Law, but also a combination of attendant phenomena which I shall 
describe presently: Figure 1 is about one-fourth the true size of the ap- 
paratus. It consists of an ordinary iron ring-stand EH, by means of which 
the various glass tubes A, B, C, and D, are held in the proper position by 
means of clamps at F. At the base is situated a Woulfe bottle G, with 
which A, B, C, D, and HE’ communicate. The bottle G is about one-third 
filled with a concentrated aqueous solution of eosin. This solution is 
readily visible and on account of its intense red color is also seen at a con- 
siderable distance in the transparent glass tubes A, B, and C. Such an 
eosin solution has the additional advantage of being rather permanent in 
color, for in two years the solution I had used did not change perceptibly, 
and only a slight reddish brown precipitate was visible. It is also quite 
resistant in the presence of HCl, and even by the use of strong HCl a 
heavy precipitate results which is almost as red for a time as the original 
solution. The glass tubes A, B, and © extend below the surface of the 
eosin solution, while D merely projects through the rubber cork H. The 
connection of all the glass tubes A, B, C, D, BH’, and L are made air-tight by 
means of the rubber corks H, and the latter are .held firmly in place by 
copper wires to prevent their being blown out of the pressure generated in 
I and G. By means of the glass tube H’ the large glass bottle I is con- 
nected with G, and another glass tube connects I with the water-tap, air- 
pump or other contrivance for generating pressure. If the apparatus is 
connected as shown in the figure to water mains carrying a high pressure, 
and if then we open the valve O, the water will be forced into I. This will 
of course cause compression of the air in I, as well as pressure in propor- 
tion to the amount of water allowed to enter. Since G is connected with 
I by EH’, the same pressure will be generated in Gas in I. As A, B, and © 
project below the surface of the eosin solution, and if the valves K and K’ 
are closed and the water continues to enter I, in a few seconds the volume 
of air in the tube C, which is sealed at the top, will be compressed one- 
half its former volume by the eosin solution rising one-half the inside 
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