PROPERTIES OF MATTER IN THE GASEOUS STATE. 
747 
Fig. 4. 
These curves bring out in a marked manner the agreement of the results with 
Law III., Art. 9. 
With air the difference rises from ‘02 of an inch ('508 millim.), at a pressure of 
30 inches, to ‘0380 of an inch or ( - 965 millim.), at a pressure of 7'5 inches, which is 
the maximum. 
With hydrogen the difference also rises as the pressure falls from 30, but the rise is 
not so great and the maximum is reached at 16 inches. 
After passing the maximum the curves both fall, and in falling obviously converge. 
This is all exactly in accordance with what was expected. 
Corresponding pressures (stucco 1, meerschaum 2). 
24. Law Y. shows that there should be correspondence between certain portions of 
the curve for stucco and those for meerschaum, although the corresponding points 
would not be at the same pressures. 
Assuming the temperatures to be the same, the corresponding points would be those 
for which the ratio of the mean pressure to the difference of pressure were the same. 
Which points may at once he found hy comparing the figures in the columns showing 
this ratio in Tables III. and IV., with the same columns in Tables VI. and VII. 
respectively. 
Before making such a comparison, however, it is necessary to introduce certain small 
corrections for the difference in the temperature of the water in the two experiments ; 
this, as will be subsequently explained, will be equivalent to diminishing the difference 
in the Tables III. and IV. in the ratio 7 to 8. 
Then we find that the pressures at whicli the ratios are the same in Tables III. 
and VI. are approximately as G to 1, taking only the higher pressures, while the 
Tables IV. and VII. give the ratio 6‘7 to 1. 
The results of this comparison, although not strictly consistent, indicate that there 
is a correspondence, the points on the curves for meerschaum corresponding with points 
on the curves for stucco, for which the pressures are about -g for air, and ( T=, for hydrogen. 
It was clear, however, that the number of observations with the meerschaum plate 
was not sufficient to allow of a very close comparison with the curve for stucco, for the 
accuracy with which the differences had been read without the cathetometer was not 
sufficient to allow of any use being made of the lower pressures. 
