336 
NATURE 
[Aug. 25, 1870 
I may, however, be permitted to make a few remarks arising 
out of Mr. Grenfell’s paper. 
" According to my view, a zzcleus is a body that has a stronger 
attraction for the gas, or the vapour, or the salt, of a super- 
saturated solution than for the liquid that holds it in solution. 
Nuclei, with certain limitations, cease to be such when made 
chemically clean. 
A body is chemically clean, the surface of which is entirely 
free from any substance foreign to its composition. 
Thus oils and fatty bodies are chemically clean, if chemically 
pure, and containing no substance, mixed or dissolved, that is 
foreign to their composition. 
The limitations above referred to are two: (1) the oils, &c., 
when chemically clean, do not act as nuclei while in the mass, 
such as a lens or globule ; but these oils, &c., whether clean or 
not, in the form of thin films, act powerfully as nuclei; (2) a 
liquid, at or near the boiling point, is a supersaturated solution 
of its own vapour, and a porous body, such as charcoal, pumice, 
&c., whether clean or not, is a powerful nucleus in separating 
vapour. 
I have on several occasions taken the liberty of opposing M. 
Gernez’s views as to the action of nuclei. He supposes (1) that 
supersaturated gaseous solutions (soda water, seltzer, &c.) give 
off their gas to nuclei by virtue of the air that these latter intro- 
duce into the solution: in other words, gas must escape into 
air, and the function of the nucleus is to carry down air ; hence 
rough bodies act better as nuclei than smooth ones, I have 
shown (Phil. Mag., August 1867) in a series of twelve experi- 
ments, that air is not a nucleus, and that rough bodies are 
inactiye, if catharised or made chemically clean. A rat's-tail 
file, for example, is a good nucleus, because it holds between its 
teeth not air, but that filmy kind of matter that is powerfully 
nuclear, and it is not easy to clean a body of this kind; but 
when clean, it is quite inactive. So, a flint stone that has been 
exposed to the air, or handled, acts as a powerful nucleus, but 
when broken, the newly-fractured surfaces are inactive, hecause 
chemically clean. And such surfaces are inactive, because the 
gaseous solution adheres to them as a whole ; whereas, if a 
Clean body be handled or exposed to the air, it becomes covered, 
more or less, with filmy matter, to which the gas adheres more 
strongly than the liquid does, and hence there is a separation. 
There is, I think, abundant proof that air is not a nucleus, its 
function, if it have any, in this class of phenomena, being that 
of a carrier of nuclei. Proof also is wanting, I imagine, that 
when a nucleus determines the crystallisation of a supersaturated 
saline solution, a salt of its own kind is present. When M. 
Gemez so laboriously prepared his nuclei, so as to free them 
from salt, he did not perhaps reflect that he was making them 
chemically clean. Of course I fully admit that, in general, a salt 
of the same kind as the solution, acts as a powerful nucleus ; 
but in order for it so to act it must adhere more strongly to the 
saline than to the liquid portion of the solution. It may even 
happen that a crystal of the same kind, and of the fully hydrated 
salt, has no nuclear action, because it is in a perfectly catharised 
condition. And here I must refer to the objection raised by 
Dr. De Coppet, that in one of my forms of showing this ex- 
periment, the hydrated crystals, say of magnesic sulphate, being 
introduced into the neck of the flask while the solution was 
boiling, and so left in the covered flask while the solution cooled, 
such crystals become so changed by the heat as no longer to 
represent the normal salt, so that when lowered into the solu- 
tion they formed a different salt, and hence were no test of the 
point in question, as to whether a salt of the same kind may be 
rendered inactiye as a nucleus. I admit the criticism to be just, 
but in my original account of the experiment (Phil. Trans., 
1868, p. 665) I did not rely upon one form only. Highly super- 
saturated solutions in clean tubes, plugged with cotton wool, 
were put, when cold, under the receiver of the air-pump, and 
left for some time 77 vacuo, over sulphuric acid, the effect of 
which was to produce crystalline crusts of the normal salt on the 
surface, and these by shaking fell through the solutions withont 
acting as nuclei; whereas on removing the cotton wool in the 
presence of air, the solutions crystallised immediately into a 
solid mass. So also by keeping supersaturated solutions during 
some months, water escapes through the cotton wool, and a 
crystalline crust of the normal salt creeps up the air-filled portion 
of the tube, and this has no nuclear character, because the ad- 
hesion between it and the solution is perfect. 
So necessary is the action of a nucleus in determining crystal- 
nuclei, highly supersaturated saline solutions may, by reduction 
of temperature to 0° F., or from that to — 10° F., be made 
solid, and by placing the tubes in snow and water at 32° F., the 
solids rapidly melt into clear bright solutions, without any 
separation of salt. These effects may be shown any number of 
times ; but whether the solution be solid or liquid, if the cotton 
wool be removed, crystallisation always sets in, in the case of 
the solid during the melting, while in that of the liquid the effect 
is immediate. 
With respect to the editorial note that the solutions of hydrated 
salts contain the anhydrous salt, I have shown in the paper last 
quoted, and with still greater elaboration in the Chemical News 
for Dec. 10th, 1869, that such is the case with respect to sodic 
sulphate. I insist on this point, as it is one of first-rate im- 
portance in considering the theory of supersaturated saline solu- 
tions. I endeavour to prove that it is the anhydrous salt in 
solution, by showing that at various points of the scale a sudden 
lowering of temperature produces a shower of the well-known 
octahedral crystals of the anhydrous salt. I also explain in my 
original memoir, that it is necessary for these erystals to be 
deposited before the modified 7-atom salt can be formed, and - 
that even when there is a copious deposit of this salt the liquor 
above it is not, as Lowel supposed, the mother liquor of the 
7-atom salt, but it is still a solution of the anhydrous salt. And 
more than this, when the sudden change in the curve of 
solubility takes place at 33° or 34° C., and there is, according to 
Gay Lussac’s supposition, a change in molecular condition, it is 
still the anhydrous salt that is in solution. 
There are several other points that might be enlarged on, 
but that I fear to trespass further on your valuable space. ? 
Highgate, N. CHARLES TOMLINSON 
Astrology 
Tue belief in astrology which still prevails among the English 
lower classes to a much larger extent than is supposed, will de- 
rive a fresh impulse from the happy guesses which have been 
made by the editor of ‘f Moore’s Almanac” in his issue for the 
current year. The hieroglyphic with which it is illustrated is less 
vague than usual, and represents two eagles fighting in the air, 
and on the plains beneath them hosts of armed men (in decidedly 
foreign uniforms) engaged in a bloody struggle. Lest the point 
should be missed, the prophet begins the forecast of the year 
with the distinct assertion that there will be war between France 
and Prussia, and that the month of July will be especially disas- 
trous to the Emperor Napoleon. Thus far events have coincided 
with the voice of the oracle, and seem to confirm the poet’s view 
that 
«The warrior’s fate is blazoned in the skies.” 
But we haye yet to see whether ‘‘ in October the King of Prussia 
(if living) will meet with defeat, and the ex-King of Hanover 
recover some of his prestige, if not his throne also,” M, Comte 
would have us deal tenderly with astrology, because it was, in 
his opinion, the first systematic effort to frame a philosophy of 
history out of the apparently capricious phenomena of aneee4 
actions. In theory we may do so, but astronomical science is 
hardly likely, for the sake of sentiment, to treasure up the dis- 
carded swaddling clothes which for so many centuries impeded 
its onward progress. 
Norton Canon, Weobley C, J. Roprnson 
On Volcanoes 
HAVING only Jast night returned from Norway, I was not 
aware before to-day that No. 40 of NATURE (August 4) con- 
tained ‘‘an outline ” of a lecture on volcanoes delivered by me 
in St. George’s Hall, Langham Place, on the rgth June (not 
gth as therein stated) last. 
Although I cannot but feel highly flattered at the length of 
this notice, I must regret that the author of this ‘* outline,” who, 
strangely enough, signs himself by my name, has, as will be 
seen upon reference to the text of my lecture as reported in the 
Geological Magazine for July, omitted every word which could 
convey to the reader the remotest idea of the object of the lecture 
itself, or the conclusions arrived at from the evidence brought 
forward. Just asa man without life is but a corpse, neither can 
a mere string of facts be called even the “‘ outline of a lecture,” 
when we have only the body without the spirit. 
The object of my lecture was to institute a comparison between 
the relative magnitudes of the operations of internal and 
lisation in these solutions, that, if care be taken to exclude | sac forces in determining the main external features of 
