Page:Scientific Papers of Josiah Willard Gibbs.djvu/420

mercury diminished the volume of the vapor, and thus increased the numbers obtained for the density.

Table II.—Peroxide of Nitrogen.
Experiments at less than Atmospheric Pressure.
Playfair and Wanklyn,—Troost,—Naumann.

Temperature		Pressure		Density calculated by eq. (10).		Density observed.				Excess of observed density.
						P. & W.	T.	N.		P. & W.	T.	N.
97.5		(301)		1.631		1.783				+.152
27		35		1.90			1.6				-.30
27		16		1.77			1.59				-.18
24.5		(323)		2.524		2.52				-.004
22.5		136.5		2.34				2.35				+.01
22.5		101		2.26				2.28				+.02
21.5		161		2.41				2.38				-.03	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
20.8		153.5		2.41				2.46				+.05
20		301		2.59				2.70				+.11
18.5		136		2.43				2.45				+.02
18		279		2.61				2.71				+.10
17.5		172		2.51				2.52				+.01	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
16.8		172		2.53				2.55				+.02
16.5		224		2.59				[2.66]				+.07	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
16		228.5		2.61				[2.62]				+.01
14.5		175		2.58				2.63				+.05
11.3		(159)		2.620		2.645				+.025
11		190		2.66				2.76				+.10
10.5		163		2.64				2.73				+.09
4.2		(129)		2.710		2.588				-.122
4		172.5		2.77				2.85				+.08
2.5		145		2.76				[2.85]				+.09
1		138		2.78				2.84				+.06
-1		153		2.83				2.87				+.04
-3		84		2.76				2.92				+.16
-5		123		2.85				2.98				+.13	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
-6		125.5		2.87				[2.94]				+.07

The same table includes two experiments of Troost,^[1] by Dumas' method, but at the very low pressures of 35^mm and 16^mm. In such experiments we cannot expect a close agreement with the formula, for the same error in the determination of the weight of the vapor, which would make a difference of '01 in the density in experiments at atmospheric pressure, would make a difference of .21 or .47 in the circumstances of these experiments. In fact, the numbers obtained differ considerably from those demanded by the formula.

There remain four experiments by Playfair and Wanklyn^[2] in which Dumas' method was varied by diluting the vapor with nitrogen. The numbers in the column of pressures represent the total pressure diminished by the pressure which the nitrogen alone would have exerted. They are not quite accurate, since the data given in the memoir cited only enable us to determine the ratios

1. Comptes Rendus, t. lxxxvi (1878), p. 1395.
2. Trans. Roy. Soc. Edinb., vol. xxii (1861), p. 463.