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F. W. Clarke on the Atomic Volumes of the Elements: 315 
ferent values, viz: 6°84 for the iron group, 9°0-92 for zinc, and 
13°6 for the cadmium group, yet in these sulphates all appear 
to possess the same atomic volume. Now it is noteworthy that 
13°6 is almost exactly twice 6:84, and zinc stands between in 
such a manner that the three values are to each other almost 
exactly as 3:4:6. Whatever may be the place of zinc in this 
series, whether accidental or not, it is certainly very remark- 
able that the metals cadmium and magnesium, forming sul- 
phates isomorphous with those of iron, cobalt, and nickel, 
should possess an atomic volume almost precisely double that 
of the latter metals. This relation must be more than a mere 
coincidence. 
_ Another point to be noticed in regard to zine and mercury 
is an exception to a rule which has seemed to hold true with 
the groups hitherto given. Between the atomic volumes pos- 
sessed by these metals in the solid state, and their values in the 
liquid condition, no direct relation is manifest. 
The platinum metals afford another remarkable instance of 
equality among atomic volumes, as has often been noticed, 
The specific gravities are as follows, according to Deville and 
Debray. Platinum 21°15, iridium 21-15, osmium 21°3-21-4, 
rhodium 1271, ruthenium 11—11-4, palladium 11-4. Their 
atomic volumes are respectively 9°3, 9°3, 9°2-9°3, 8°5, 9:1-9°4, 
and 9-3, The average is 9°15, almost exactly the value for zinc, 
although this is probably a mere coincidence. A revision of 
the sp. gr. of rhodium will probably place it lower, and increase 
the atomic volume, so as to make the value for this group 
about 9-3, 
Molybdenum and tungsten afford another well known exam- 
ample of equality. The sp. gr. of the first is 8-64, (Bucholz,) 
and that of the second from 16°54—18-447, according to the 
State of agereeation and mode in which it was prepared, accor- 
ding to the observations (independent of each other) of Van 
Slar an ettnow. atomic volume of molybdenum is 
therefore 11-2, and that of tungsten from 9°9-11'1. If instead 
of 111-112, we place the value for these metals at 11-4, we 
find that the latter number falls into a vacant place in the iron, 
zinc, and cadmium series, standing in that series so as to make 
the four values to each other as 3:4:5:6. This may be 
accidental, however. : 
The equality between silver and gold is also well known, 
the atomic volumes of these two metals being represented by 
the number 10-2. : ae 
A noteworthy relation to oxygen is found in the atomic vol- 
umes of the remarkably similar elements calcium, barium, 
Strontium, and lead, The sp. gr. of calcium is 155 (Liés Bodart 
