186 F. W. Clarke on Atomic volumes of Liquids. 
free from an excess of water, the strongest containing only 
about 97 per cent of monohydrate ; and therefore its atomic 
volume, as deduced from its vapor volume, is undoubtedly a 
trifle too low. Be that as it may, however, in these two com- 
pounds I obtained as the atomic volume of selenium the num- 
bers 24°7 and 21:8, the mean being 23:2. This is only 06 
greater than the number given by Kopp as the lower atomic vol- 
ume of sulphur, and, therefore, taking into account that sul- 
phur and selenium in the solid condition have equal atomic vol- 
umes, it seems almost certain that the same equality holds true 
in their liquid compounds. 
I determined the vapor volumes of two lead compounds, lead 
tetrethyl and lead triethyl, but, to my great surprise I obtained 
the same number for both. This isso anomalous that I am 
inclined to think either that there is an error in the numbers 
