IIo 

for the measured compressibility, and finds that this 
force may be written F=)/8", where 6 and mn are 
constants and 6 is the distance between neighbouring 
ions of the same kind. For sodium chloride and other 
halogen-alkali compounds 7=9. The law of force thus 
obtained is used to calculate the energy produced by 
the union of the ions to form the salt, which for one 
“Mol” is U=545° /p/(u,+p_) kg. cal., where py 
is the atomic weight of the metal and j_ that of the 
halogen. For absolute zero U,,,=158, Ux,=144, when 
the ions are at rest in the position of equilibrium. 
Nernst has shown that, if U is known, the chemical 
affinity at any temperature can be determined from 
purely physical considerations. These results can be 
checked by measuring the heat of solution of the salts, 
in solutions so dilute that dissociation is complete, and 
calculating the heat produced in such reactions as 
NaCl+ KI=Nal+KCl. The values obtained were 
of the same order as those calculated by the above 
theory, but depend only on the differences between the 
values of U. 
Another method of attacking the problem is to use 
Bohr’s theory of atomic structure and radiation to find 
the work required to form ions from neutral atoms. 
Franck and Hertz have deduced that the energy of 
ionisation I=hy o , where h is Planck’s constant and 
v co is the limit of the series of absorption spectrum lines 
of the quiescent vapour. These workers have con- 
firmed this theory by measuring the ionising potential 
which must be applied to a stream of electrons to 
produce a velocity just capable of ionising the vapour. 
They have thus found the energy of ionisation of a 
number of substances. Combining these values with 
values of the affinity for electrons of electro-negative 
atoms obtained by Franck, who used a method also based 
on Bohr’s theory of the spectrum, the values of U can 
be calculated independently, and are within 12 per 
cent. of those obtained from the compressibility data. 
Habers has studied metal crystals, on the assumption 
that the negative atoms in the Bragg space lattice are 
replaced by electrons. He finds for the alkali metals 
n=2°5 tO 3°4, copper m=8-0, silver m=g-0, in the 
expression for the repulsion. The heats of vaporisa- 
tion calculated from these figures agree remarkably well 
with the observed values. The value of m must depend 
upon the distribution of the electrons in the ion. 
The author seems perfectly justified in concluding 
his work in the following words: “If we survey the 
road we have travelled we see that, although it has not 
yet penetrated very far into the mighty kingdom of 
chemistry, it has reached a point from which we can 
observe, in the distance, the passes over which we shall 
have to travel if we wish to subject this kingdom to 
physical law.” 
NO) 2778, VOL. 111 
NATURE 

[JANuaRY 27, 1923 

Bauxite in Ayrshire. 
Memoirs of the Geological Survey, Scotland. The 
Ayrshire Bauxitic Clay. By,» G. V. Wilson. Pp. 
vi+28. (Southampton: Ordnance Survey Office ; 
London: E. Stanford, Ltd., 1922.) 1s. 6d. net. 
HILE deposits of bauxite, that is, of the 
aluminium hydroxides gibbsite and diaspore, 
are greatly in request as sources of aluminium, bauxitic 
clays are also of considerable value for the lining of high- 
temperature furnaces. It is well known that under 
tropical conditions of weathering, especially where the 
surface-waters are alkaline, rocks of very varied nature, 
containing aluminium silicates, yield bauxite rather 
than kaolin. Any ferruginous matter forms at the same 
time lateritic crusts. Laterite, indeed, as Sir Thomas 
Holland pointed out for India, is at times rich in 
aluminium hydroxide. 
Bauxitic formations have thus come to be regarded 
as indications of climate in the past, and we now have 
the interesting discovery of bauxitic clays in strata 
of Millstone Grit age in Ayrshire. The lateritic nature 
of these Carboniferous beds was pointed out by Mr. John 
Smith in the Transactions of the Geological Society of 
Glasgow in 1893. The Geological Survey of Scotland, 
when recently remapping the area, collected samples 
for analysis and proved the presence of aluminium 
hydroxide. Mr. Wilson, in the memoir now published, 
defines a bauxitic clay (p. 6) as one that “ contains 
more alumina than is necessary to supply the demands 
of the whole of the silica present for the formation of 
the kaolinite molecule.’ Silica present in the form 
of quartz sand is included in this definition, since such 
silica affects the value of a clay as a refractory material. 
On p. 25 twelve analyses are given of the Ayrshire 
bauxitic clays. The most striking of these is that of 
the bed on the Saltcoats shore, which yields 47-57 
per cent. of alumina and only 29:0 per cent. of silica. 
Titanium dioxide, a substance characteristically pres- 
ent, amounts, however, to 9:04 per cent., and the re- 
fractory quality of a kaolinite clay is said to be lowered 
by 5 per cent. and upwards. This effect is not so 
noticeable in clays with an excess of alumina. In the 
Ayrshire deposits, a large part of the material of 
inferior grade reaches a refractory quality of 30-31 on 
the Seger cone scale, while the Saltcoats shore material, 
despite its titanium-content, is recorded as over 35. 
These bauxitic clays have been derived from basaltic 
lavas in the first instance, though in some cases the 
material has been transported. It is held that kaolinite 
was formed as the earliest product, and that a fairly 
pure aluminium hydroxide arose from this, sometimes 
with an oolitic structure. A recombination of the 

