SECTIONAL TRANSACTIONS.—B. 433 
perties are not intermediate between those of zirconium and thorium, but much 
nearer to the former element. 
While the fluorides and double fluorides of thorium are practically insoluble, 
the corresponding zirconium compounds, and still more the hafnium compounds, 
are fairly soluble in cold, very soluble in hot water. By this method zirconium 
can easily be separated from hafnium. ‘lhe mineral is melted with KFHF, 
and by crystallising the potassium double fluorides the hafnium concentrates in 
the mother-liquor. Most of the preparations exhibited have been obtained by 
this method. 
Hafnium oxalate is, like zirconium oxalate, soluble in an excess of oxalic 
acid. The oxychloride of hafnium is less soluble than zirconium oxychloride. 
When crystallising compounds of zirconium sulphuric acid like (NH_,),[Zr(SO,),]; 
(NH,),[Zr,(OH),(SO,),] hafnium concentrates in the mother-liquor. Hafnium 
is more basic than zirconium; accordingly the latter is more easily precipitated 
by ammonia, sodium thiosulphate, &c.; and while zirconium sulphate begins 
to decompose above 400°, the temperature at which hafnium sulphate undergoes 
-a marked decomposition lies about 100° higher. Thorium phosphate is easily 
dissolved by strong mineral acids, zirconium phosphate much less, whereas 
hafnium phosphate is found to be still less soluble. 
The close relationship of zirconium and hafnium is also clearly exhibited by 
the fact that zirconium extracted from different minerals always contains 
4-30 per cent. hafnium, while in none of the typical thorium minerals could 
hafnium be detected. We must conclude that ‘zirconium,’ hitherto thought 
to be an element, is a mixture of two elements, of zirconium and hafnium. 
8. Joint Discussion with Section I on The Physical Chemistry of 
Membranes in Relation to Physiological Science, opened by 
Prof. H. E. Roar. 
9, Dr. E. B. R. Prmraux.—Membrane Potentials considered as 
Diffusion Potentials. 
Through most ordinary membranes, such as vegetable and animal parchment, 
&e., a slow diffusion of electrolyte takes place, and the membrane potentials at 
these are not due to the impermeability, but to the selective permeability, of 
either anion or kation. These potentials are generally higher than the corre- 
sponding diffusion potentials, and may be considered as diffusion potentials 
in which the transport numbers or the relative mobilities of one ion are modified 
by the membrane. A suitable case already investigated was that of sodium 
benzoate. The investigation has now been extended to potassium benzoate 
and salicylate. A comparison of the mobility of the anion determined by con- 
ductivity with the present measurements of diffusion potentials, viscosities, 
and membrane potentials, shows that the mobility of the benzoic anion has 
indeed been diminished by the parchment to a value which is apparently definite 
_ both for potassium and for sodium salts. The mobility of the salicylic ion has 
been diminished in a higher ratio. : 
10. Miss Epirn H. Usnerwoopv.—The Activation of Hydrogen in 
Organic Compounds. 
In the first part of this paper it is shown that a great variety of organic 
~ chemical phenomena depends upon one and the same molecular condition. This 
condition is then defined in terms of molecular structure, and the result follows 
that tendency to undergo reactions of many different kinds is referred to certain 
definite and easily recognised structural features. Thus, without instituting 
any proposal as to the root cause of organic reactions, and with a minimum of 
tacit hypothesis, a collation of diverse data is obtained, and, in addition, an 
instrument for the prediction of new phenomena. 
The usefulness of the view in this latter connection is illustrated by reference 
to certain phenomena predicted from theory, and experimentally verified by 
the author within the last few months (e.g. the formation of rings with the aid 
of the nitroso group; the reversibility of the aldol reaction), and also by noting 
hitherto unverified consequences, on which the author hopes, to obtain evidence 
in the immediate future, 
GG2 
