1885.] 
The Composition of Sewage ; 385 
Mercury freezes near — 40° C., a characteristic tempera- 
ture for vapour of water tension (ref.) ; it boils about 360° C. ; 
its evaporation becomes perceptible beyond 32 0 C. The 
change of temperature between freezing and boiling of water 
is 100 C. ; it is 400 for Hg, four times more ; for ocean 
water 3*83 times more. Water expands by freezing, 
14-12-08 (polar zone of the hemisphere), and from o° to 100° 
14-24-016, with greatest contraction at 4-13° C. (ref.). 
Mercury expands for each degree between o° and ioo°, the 
i-^- 555 °> towards —40° less, towards 360° more. Hg there- 
fore expands, for equal change of beat, 2 to 1*95 less than 
water or ocean water, or ' 4 to ^3-83 less. Hg expands 
from state to state 14-12-08, the double of water.* The 
densities of Hg being 13-88 at 4 0 C., and 14-39° at -40° C., 
the density of solid Hg is 3-83* = 14-66 that of water— 
diff. 14-59-56 (ref.). 
This shows a curious similarity and reciprocity between 
Aq and Hg. Is mercury a large atom combined with H ? 
In the original paper there were remarks about the 
making and unmaking of elements, and propositions for 
experiments with I, Br, Chi, and Hg ; but being no experi- 
mentalist I had better abstain from such suggestions. 
II. THE COMPOSITION OF SEWAGE. 
By J. W. Slater. 
TRANGE to say even professed sanitarians, municipal 
authorities, and the like, not to speak of educated 
and intelligent people in general, have often very 
vague notions concerning the nature of sewage. They know 
that it is nasty, and contains various matters unsightly and 
offensive. But they are little aware of its complexity and 
of its liability to vary, according to the locality, the season, 
and even the hour of the day. Were these points better 
* Water expands 1412-08 when become ice; mercury contracts about 
1 4 12-08. Bi is said to expand when again become solid after liquidity at 265° C 
(Marx), but this may be not quite true, as pointed out in “On the Atom.” 
