ew) 
a | 
— 
length of the tube when the pressure in G equals one atmosphere. This 
illustrates Boyle’s Law by showing that the volume of gas in © varied in- 
versely as the pressure brought to bear upon it. ‘The same principle would 
be shown in A and B under similar circumstances if IX and WK’ of the tubes 
M M’, which are fastened to A and B by means of rubber tubing held by 
copper fire and sealing-wax, remained closed. 
Again, when the air in A, B, and © is compressed one-half its volume 
by a pressure of one atmosphere, this will be shown by the manometer 
which the tube D forms. This tube has each of its two arms filled to a 
height of forty centimeters with mercury. The total height of the two 
columns is therefore equivalent to more than an atmosphere. When the 
pressure in G is zero, then the two columns of mercury X and Y are equal 
in height. When, however, the pressure in G is equal to one atmosphere, 
then the column X will sink and column Y will rise till the difference of 
their heights is 76 e«m. Since, in estimating accurately the height of a 
mercury column both pressure and temperature must be considered, this 
may be done by the usual formula. 
When it is desired to again reduce the pressure in G to zero and allow 
the water in I to escape, this may be done by closing O, opening P, and 
either IX or K’, or both. Unless I is interposed between O and G, water 
could not for obvious reasons be used. Air could, of course, be forced di- 
rectly into G. 
The apparatus can also be used to show that the height to which a 
liquid will rise in a tube is independent of its diameter. If we open O 
then, as mentioned above, the pressure developed in I and G will cause the 
eosin solution to rise with ease in A and B if K and XK’ are left open. 
When the eosin solution has risen to 8, or to any other height in B, whose 
internal diameter is three millimeters, then if we notice A, disregarding 
the small effect of capillarity in B, the column of liquid will stand at ex- 
actly the same height in A, whose internal diameter is one cm., as in B. 
If, finally, both A and B are rapidly filled with the eosin solution by 
quickly and strongly generating pressure in G, then it will be seen by 
carefully timed observations that the liquid in A will rise to an equilibrium 
of the pressure in G somewhat more quickly than the same equilibrium 
will be attained by the liquid in B, due to the greater friction produced by 
the smaller tube B. For the same reason if the pressure is rapidly re- 
duced to zero by opening P, the eosin solution in B will require a slightly 
longer time to fall from a point, as S, and reach the level of the liquid 
in G, than would be required by the same height of a column in A, 
State University, Bloomington, Ind. 
