| Sept. 25, 1873] 
distance between any two of its points. It appears to the Com- 
mittee that it is not advisable to introduce redundant axioms ; 
but that all the assumptions made should be necessary for de- 
monstration of the propositions, and independent of one 
another. 
It appears that the Principle of Superposition might advan- 
_ tageously be employed with greater frequency in the demonstra- 
tions, and that an explicit recognition of it as an axiom of fun- 
damental assumption should be made at the commencement, 
The Committee think also that it would be advisable to intro- 
duce explicitly certain definitions and principles of general logic, 
in order that the processes of simple conversion may not be con- 
founded with geometrical methods. 
3. The Syllabus of the Geometrical Association. 
The Association for the Improvement of Geometrical Teaching 
has issued (privately) a Syllabus covering the ground of the first 
four hooks of Euclid. The Committee are of opinion that the 
Syllabus is decidedly good, so far as it goes, but they do not 
wish to make a detailed report upon it in its present incomplete 
state. When it is finished, however, they will be prepared to 
report fully upon the merit of its several parts, to make such 
suggestions for revision as may appear necessary, and to discuss 
the advisability of giving to it the authority of the British 
Association, For this purpose the Committee request that they 
may be reappointed. : 
SECTION B,—CHEMISTRY 
A report on Zssential Oils, prepared by Dr. Wright and Dr. 
Gladstone, was read by the former. 
On Black Deposits of Metals, by Dr. Gladstone, F.R.S. 
If one metal be thrown down from solution by means of 
another metal, it does not always present itself of the same 
colour as it exhibits when in mass; in fact, most metals that 
are capable of being precipitated by substitution may be obtained 
ina black condition. The allied metals, platinum, palladium, and 
iridium, are generally if not always black when thus precipitated, 
and bismuth and antimony form black fringes and little else. 
Similar fringes are also formed by gold, but it also yields green, 
yellow, or lilac metal according to circumstances. Copper, 
when first precipitated on zinc, whether from a weak or asirong 
solution, is black ; but in the latter case it becomes chocolate- 
coloured as it advances, or red if the action be more rapid. 
Lead, in like manner, is always deposited black in the first in- 
_ Stance, though the growing crystals soon become of the well- 
known dull grey. Silver and thallium appear as little bushes 
of black metal on the decomposing plate, if the solution be very 
weak; otherwise they grow of their proper colour. Zinc and 
cadmium give a black coating, quickly passing into grey when 
their weak solutions are decomposed by magnesium. ‘The gene- 
ral result may be stated thus: If a piece of metal be immersed in 
the solution of another metal which it can displace, the latter 
metal immediately makes its appearance at myriads of points in 
a condition that does not reflect light ; but as the most favour- 
ably circumstanced crystals grow, they acquire the optical pro- 
perties of the massive metal, the period at which the change 
takes place depending partly on the nature of the metal and 
partly on the rapidity of its growth. In the production of the 
black deposit of the copper-zine couple lately employed by the 
' author and Mr, Tribe to break up various compound bodies, 
there are several stages that may be noticed. At first an out- 
growth of copper forms on the zinc ; then, while this action is 
still proceeding, the couple itself acts upon the water or the sul- 
phate of zinc in solution, the metallic zinc being oxidised, and 
hydrogen gas or black zinc being formed against the copper 
branches. This deposit of zinc was originally observed by Dr. 
Russell. The arrangement of the particles between the two 
metals in connection is supposed to be somewhat thus :— 
Cu | Zn SO, | Zn SO, | H,O | H,O | Zn 
which, by the conjoint power and chemical force, becomes— 
Cu| Zn| Zn SO, | H, SO,| H,O| Zn 
If there is still copper sulphate in the solution, this deposited 
zinc may in its turn become coated with copper, but if it remains 
exposed to water it is sure to become oxidised. The black de- 
osit often assumes a brownish colour when this is the case. 
he copper on which zinc has been deposited gives a brassy 
streak when rubbed in a mortar ; but the presence of oxide tends 
to prevent the sticking together of the detached pieces of metal, 
NATURE 
453 
and thus the formation of a streak on pressure. If, however, the 
oxide be removed by acetic acid, the clean ramifications of metal, 
whether black or otherwise, conglomerate of their own accord 
in a remarkable way, and little pressure is required to obtain a 
yellowish metallic streak ; while if hydrochloric acid be used, 
the zinc itself also dissolves with effervescence, and the con- 
eoenaene pieces of metal, when rubbed, give a coppery 
streak, 
The Secretary read a paper communicated by Mr. Tribe, Ox 
an Improved Specific Gravity Bottle. The apparatus was origi- 
nally designed for taking the specific gravity of inflammable 
liquids, but, as the President explained, it might be used for any 
other class of liquids. 
Mr. W. H. Pike read a?paper on Several Homologues of Oxa- 
luric Acid, 
The anhydrides of dibasic acids combine with urea and sulpho- 
urea to form bodies which have the general formula. 
CO—NH—CO—NH, 
RS . 
\coou 
have been obtained are— 
The acids in this series which 
CH,—CO—NH—CONH, 
Succino-carbaminic acid, | 
CH,—COOH. 
: CH,—CO—NH—CSNHz 
Succino-sulpho-carbaminic acid, | 
CH,—COOH. 
/oO-NE. CS.NHz, 
Citracon sulpho-carbaminic acid, C3Hy 
\coou. 
Dr. Wright read a paper on Vew Derivatives of Codeine and 
Morphine. 
It was a résumé of the results obtained in the previous year in 
continuation of those brought before the Association on former 
occasions. Morphine gave rise by treatment with sulphuric acid 
to polymerides precisely analogous to those obtained from codeine 
under similar conditions. Trimorphine and tetramorphine had 
been isolated, but di-moiphine had not yet been formed. Deri- 
vatives from these bodies by the action of hydrochloric acid had 
been obtained and extended. By the action of hydrochloric acid 
on morphine a chlorinated product had been formed. By 
further treatment this formed apomorphine, a new body. Under 
the same circumstances codeine gave rise to a chlorinated base 
homologous with that from morphine. But further action gave 
rise not to the apomorphine, but to a somewhat similar body 
containing more of the elements of water. The action of zinc 
chlorides on morphine had also been examined ; the final pro- 
ducts were apomorphine and an isomeric base of the tetra series, 
intermediate substances being formed. The physiological pro- 
perties of most of these new derivatives had been stated, and 
some connection made out in certain cases between the composi- 
tion and the physiological action. 
friday, September 19 
The report of the Committee for superintending the Monthly 
Reports of the Progress of Chemistry was read. The report bore 
testimony to the great good which the publication of the abstracts 
of chemical papers by the Chemical Society had already effected, 
and in the discussion which ensued it was stated that amongst 
the purposes to which the Association applied its funds, there 
was none which had proved more useful than this grant. 
The report of the Committee on Siemens’s Pyrometer was read 
by Prof. G. C. Foster, F.R.S. 
The experiment of which the results were communicated to 
the Chemical Section of the Association in the Report pre- 
sented last year, having shown that the exposure of the Pyro- 
meter to a red heat caused an alteration of the Zero-point of the 
instrument, which was attributed by Prof. Williamson, in conse- 
quence of experiments on the behaviour of platinum heated in 
contact with silica in an atmosphere of carbonic oxide, to the 
chemical alteration of the platinum of the pyrometer-coil due to 
the joint action of the silica of the porcelain core on which the 
wire was wound, and of the reducing atmosphere existing inside 
the prosecting iron tube. Mr. Siemens supplied the Committee 
with two pyrometers, in which, in order to guard against the 
cause of change above-mentioned, the platinum coil was incased 
in a platinum tube placed inside the outer iron tube. The ex- 
