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was very slight, but at the end of half an hour a faint
purple deposit was seen both on the glass plate and on
the walls of the tube. On removing the rod from the
apparatus it was seen that the portion which had been
covered by the small glass tube retained its original purple
appearance, while the part that had been exposed to elec-
trical a^on had changed to the dull white colour of
aluminium. Examined under the microscope, the whitened
surface of the Austen alloy was seen to be pitted irregu-
lariv, with no trace of crystalline appearance.

This experiment shows that, from an alloy of gold and
aluminium, the gold is the first to volatilise under elcArical
influence, the ammininm being left behind. The purple
colour of the deposit on glass is probably due to finely-
divided metallic gold. The first deposit from a negative
pole of pure gold is pink ; this changes to purple as
the thickness increases. The purple then turns to green,
which gets darker and darker until the metallic lustre of
polished f;old appears.

Returning to the analogy of liquid evaporation, if we
take several liquids of different boiling-points, put them
under the same pressure, and apply the same amount of
heat to each, the quantity passing from the liquid to the
gaseous state will differ widely in each case.

It was interesting to try a parallel experiment with
snetals, to find their comparative volatility under the same
conditions of temperature, pressure, and eledrical in-
fluence. It was necessary to fix upon one metal as a
atandard of comparison, and for this purpose I seleded
gold, its eledrical volatility being great, and it being easy
to prepare in a pure state.

An apparatus was made that was praAically a vacuum
tube witn four negative poles at one end and one positive
pole at the other. By a revolving commutator I was able
to make ele^rical connedion with each of the four nega-
tive poles in succession for exadly the same length of
time (about six seconds) ; by this means the variations in
the strength of the current, the experiment lasting some
hours, affeded each metal alike.

The exposed surface of the various metals used as
negative poles was kept uniform by taking them in the
form of wires that had all been drawn through the same
atandard hole in the drawplate, and cutting them by
gauge to a uniform length; the aAual size used was
0*8 m.m. in diameter and 20 m.m. long.

The comparison metal gold had to be used in each
experiment ; the apparatus thus enabled me to compare
three different metals each time. The length of time
that the current was kept on the revolving commutator
in each experiment was eight hours, making two hours
of eledrification for each of the four negative eledrodes ;
the pressure was such as to give a dark space of 6 m.m.

The fusible metals, tin, cadmium, and lead, when put
into the apparatus in the form of wires, very quickly
melted. To avoid this difficulty a special form of pole
was devised. Some small circular porcelain basins were
made, 9 m.m. diameter ; through a small hole in the
bottom a short length of iron wire, 0*8 m.m. in diameter,
was passed, projeding downwards about 5 m.m. ; the



basin was then filled to the brim with the metal to be
tested, and was fitted into the apparatus exadly in the
same way as the wires ; the internal diameter of the
basins at the brim was 7 m.m., and the negative metal
filed flat was thus formed of a circular disc 7 m.m.
diameter. The standard gold pole being treated in the
same way, the numbers obtained for the fusible metals
can be compared with gold, and take their place in the
table.

The following table of the comparative volatilities was
in this way obuined, taking gold as ■> 100 :—

Palladium xo8*oo

Gold .. luo'oo

Silver .. •• 82'68

Lead 75*04

Tin 56-96

Brass 51*58

Platinum 44*oo

Copper 40*24

Cadmium • 31*99

Nickel 10*99

Iridium .. •• •• ... 10*49

Iron • 5*50

In this experiment equal surfaces of each metal were
exposed to the current. By dividing the numbers so
obtained by the specific gravity of the metal, the following
order is found : —



Palladium
Silver ..
Tin ..
Lead ..
Gold ..
Cadmium
Copper
Platinum
Nickel..
Iron . .
Iridium



9*00

776

6*6i
5'i8

37a
2*52
2*oa
1*29
0*71
o*47



Aluminium and magnesium appear to be pradically
non-volatile under these circumstances.

The order of metals in the table shows at once that
the eledrical volatility in the solid state does not corre-
spond with the order of melting-points, of atomic weights,
or of any other well-known constant. The experiment
with some of the typical metals was repeated, and the
numbers obtained did not vary materially from those
given above, showing that the order is not likely to be far
wrong.

It is seen in the above table that the eledrical volatility
of silver is high, while that of cadmium is low. In the
two earlier experiments, where cadmium and silver were
taken, the cadmium negative eledrode in 30 minutes lost
7*52 grs., whilst the silver negative eledrode in x| hours
only lost 0*19 gr. This apparent discrepancy is easily
explained by the fad (already noted in the case of cad-
mium) that the maximum evaporation cfied, due to
eledrical disturbance, takes place when the metal is at or
near the point of liquefadion. If it were possible to
form a negative pole in vacuo of molten silver, then the
quantity volatilised in a given time would be probably
much more than that of cadmium.

Gold having proved to be readily volatile under the
eledric current, an experiment was tried with a view to
producing a larger quantity of the volatilised metal. A
tube was made having at one end a negative pole
composed of a weighed brush of fine wires oi pure gold,
and an aluminium pole at the other end.

The tube was exhausted and the current ^m the
indudion coil put on, making the gold brush negative ;
the resistance of the tube was found to increaae consider-
ably as the walls became coated with metal, so much so
that, to enable the current to pass through, air had to be
let in after a while, depressing the gauge | m.m.

The weight of the brush before experiment was



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Association versus Dissociation in Solutions ^



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35*4^40 gn. The indudion current was kept on the tnbe
for X4I hours ; at the end of this time the tube was
opened and the brush removed. It now weighed 32*5613,
showing a loss of 2*9327 grs. When heat^ below red-
ness the deposited film of gold was easily removed from
the walls of the tube in the form of very brilliant foil.

After having been subjeAed to eledrical volatilisation,
the appearaDce of the residual piece of gold under the
microscope, using a 4-inch objeA-glass, was very like
that of eleiftrolytically deposited metal,, pitted all over
with minute hollows.

This experiment, on the volatilisation of sold having
produced good coherent films of that metaJ, a similar
experiment was tried, using a brush of platinum as a
negative eledrode. , On referring to the Uble it will be
seen that th^ , ele^cal volatility of platinum is much
lower than thai of gold, but it was thought that by taking
longer tin^e a sufi^cient.qu^intity might be volatilised to
enable it to be removed ^om.the tube.

The vacuum tube, was exhausted to such a point as to
give a dark space of 6 m.m.^ and it was found, as in the
case of gold, that as a coating of metal was deposited
upon the glass the resistance rapidly increased, but in a
much more marked degree, the residual gas in the tube
apparently becoming absorbed as the deposition pro-
ceeded. It was necessary to let a little air into the tnbe
about every jo minuteSt to. reduce the vacuum. This
appears to show that the platinum was being deposited in
a porous spongy fonn, with. great power of occluding the
residual gai*..

Heating the tube wh^n it had become this way non-
condudting liberated sufficient gas to depress the gauge
of the pump z m.ip,, and to reduce the vacuum so as to
give a dark space q( about 3 m.m. This gais was not re-
absorbed on cooling, but on . pasting the current for ten
minutes the . tube again refused to conduct, owing to
absorptioi^* The tube was again heated, with another
liberation of gas, but much less than before, and this
time the whole was re-absorbed on cooling.

The current was kept on this tube for 25 hours ; it was

' then opened, but I could not remove the deposited metal

except in small pieces, as it was brittle and porous.

Weighing the brush that had formed the negative pole

gave the following results : —

Grains.

Weight of platinum before experiment • • 10*1940
„ ' „ after experiment .. 8*1570

Lots by volatilisatton in 25 hours •• •• 2*0370

Another experiment was made similar to that with gold
and platinum, but using silver as the negative pole, the
pure metal being formed into a brush of fine wires. Less
gas was occluded during the progress of this experiment
tnan in the case of platinum. The silver behaved the
same as gold, the metal deposited freely, and the vacuum
was easily kept at a dark space of 6 m.m. by the very
occasional admission of. a trace of air. In 20 hours
nearly 3 grs. of silver were volatilised. The deposit of
silver was detached without difficulty from the glass in
the form of brilliant foil.



A NOVEL METHOD FOR THE PRODUCTION

OF SODIUM AND POTASSIUM NITRITE.

By H. N. WARRBNf Research Analyit.

Thb surface, or catalytic adion, which platinum exerts
upon ammonia when in the presence of oxygen, with the
produdion of the white cloud of ammonium nitrite, is,
when catrefully peformed, more than striking as regards
the quantity of nitrite thus formed, but by employing a
more energetic form of plaUnum the effeAs may be con*
siderably enhanced.
The most powerful surface adion that I have been



succeeslul in producing was obtained as follows:—
Platinum was dissolved by the aid of aqua regie,
evaporated to dryness, and tne resulting platinic chloride
thus formed maintained at a temperature of 400* F. as
long as any chlorine continued to be evolved ; the residue
was now boiled with a slight excess of sodium carbonate,
and the platinic hydrate thus produced dissolved by
means of oxalic acid, the solution coocentrated, and a
sufficiency of asbestos yam added to absorb the solution ;
the yam, which now measured about ayard in length, when
dried and ignited contained about xa per cent of platinoa,
presenting a grey colour charaderistic of that metal
when in the spongy form, the asbestos meanwhile retain-
ing its original ropy properties without becoming brittle,
as is the case when platinic chloride is used in place of
the oxalate. The so-prepared asbestos Was next intro-
duced into a combustion-tube somewhat longer than the
same, and conneded to an appatratus evolving ammonia
gas : a current of air being at the same time injeded ^to
the apparatus, in order to furnish a mixture of oigpgen
and ammonia, the adion of the platinised asbestos was
now started by appljring the flame of a Bnnsen burner to
the more remote end of the tube. Dirodly the mixed
gases are allowed to impinge upoKU tbe^ilatinised surface,
dense clouds of ammonium nitrite are evolved, and in
several instances the whole length of the asbeslosr- be-
came intensely heated, the ammonieiti nitrite tbas46mied
being conveyed into a solution of oaasti« soda^ and« -by
so doing, producing an equivalent of sodium nitrites the
ammonia thus evolved being retained for a further supply
of ammonium nitrite.

Some idea as to the delicacy of this so^prepared
asbestos can be obtained when I mention that for several
minutes, while the apparatus was in complete working
order, scarcely any excess of ammonia could be deteded
at the further end of the tube, the whole of it being con-
verted into that of nitrite.

Bverton Research Laboratory,,

z8, Albion Street, Bvectoo, Liverpool.



ASSOCIATION VERSUS DISSOCIATION

IN SOLUTIONS.*

By SPBNCBR UMPRBVILLB PICKBRINO, M.A^ F.R.S.

Thb view that eledrolytes in aqueous soletiens' ere
partially dissociated into their ioni is chiefly based on
the corredness of the evidence as to the ntimber nCeoele-
cules or ading units present afibrded by the de pr ess i on
of the freesing-point of the solvent. If this method is
reliable, it will afford consistent evidence in whatever way
it may be applied.

When 5H2SO4, for instance, are dissolved in isHjO,
some of the acid molecules become dissociated according
to the modem physical theory of solution, so thes the
solution conslsu of more Hum twenty ading units ;
according to the hydrate theory, on the oUier faaad^ the
acid and water combine together to a cettain. extent, so
that the solution consists of U$s than twenty ediag tnits.
By adding this solution to some other crystaftlisable lignid,
such as acetic acid, we can, according to the physical Iheery*
determine the number of ading units of wtach itisoom-
posed ; and the result shows that, instead of ooosistiog of
more twenty ading units, it consists of ooly 6*5 eftits*
Thus the very phenomenon on which the physical theoiy
is based gives most emphatic evidence against that
theory.

The sulphuric acid and water together prodece a
smaller depression of the freezingwpoint e£ acetic add
than the water alone does, so that o* adding- solphtiffic
acid to dilute acetic add, the freesing>^poiet of the Utter
is adually raised. A series of det e r a i iea tieas tres asade



* Abetraa of a Paper read before the German Oheiaical Society.



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^^jS2^f5?^ \ ^ mmontum Selentte for Diagnosis of the A ikaloids.

— f ' ' ■ — • ___ _



jiip mkiich,(li£fcceii| Amouatt of sulphuric acid were added
to weak acetic acid, and the results gave the data
requisite for the construdioo of the following table, in
which the depression aAually produced by the water and
tulphuric acid is compared with that which would be
pnidnced if these two aAed independently.* In the

*t extreme qase the observed depression amounts to only
one-third of the calculated value.



If ol«eBl«r *M


DspKuion


for 14-4 H,0+(*-l4-4)H.SO^.


too CtH«Os


« jr.


CalcoUted.


Found.


Difierence.


X4-4




• • ~~"


— >





15 'o




.. 6-76»


5V


— x*ii*-ii6 p.c.


175




.. 8*00


377


- 4-23 -53 ..


'20




9*08


2'95


- 613 -68 M


^5




•• "-53


3'45


- 908 -73 „


30




.. 1709


6*oo


-xi-09-65 „


.35




•• 2470


965


-1505 -6x „


40




00


14*00


00


^^




00


X9-I5


00


'50




00


26*00


00


55




00


39-30


•0



, In these determinations the mimmiim proportion of

' iulpboric acid to water correspoaded to that of a 40 per

cent sohxtion, and such a solution is held to bel^ave

aaomalouslyt owing to its strength being too great for the

corred' application of Van t' HolPs theory of the lowering

'of the freesing-point. On plotting out all the results,

' however, it was evident that the phenomenon which they

-tohibited would also be exhibited by solutions containing

' a far smaller proportion of sulphnric acid ; but to remove

• altdottbt that this was the case, the following determina-

' tkma were made : —





Molecolet


of






Water


+ Sulphuric acid »


Total






To 100 (C,U


•OJ.






x6-8


+


B


i6-8


7-3a*


168


+ 0-0x7


OB


x6'827


733


168


+ 0035


a


16-835


rx8


X6-8


+ 0054


wm


16-854


7x6


16-8


+ 0097





X6-897


703



• In the second and third of these determinations the

' snipbnric acid and water form solutions containing only
or and 0*6 per cent of the former respedively, and such
solutions, Arrhenius maintains (Cbbm. News, Ixiii., X48),
behave in strid accordance with the dissociation and

' osmotic pressure theories. Each molecule of acid be-
comes, according to him, dissociated into 2*X4 ions (on

^the average), forming, that is, x*X4 more ading units than
were present before the dissolution. Yet the present
determinations show that this is not the case ; the
number of ading units is diminishid by o*2X and 0*32 in
the two cases, instead of being inerta^td by i*X4.
Other substances which possess a strong ajffinity for

'water behave like suiphurie acid, and adually raise the
fireeaing-potnt of weak acetic acid. This was found to be
- the case with hydrochloric acid to a very marked extent,
and in a smaller degree with calcium chloride. With
phosphoric acid there was no raising of the freesing-point
of weak acetic acid of the strength which was taken, but
the additional lowering produced was almost nil — that is,
' the water and phosphoric acid caused a depression
vcsarcely in excess of that caneed by the water only. With
nitric acid the additional depression was considerable, but

' yst It was notably smaller than that which would be pro-
duced if no commnation between the water and acid had



291

represents the whol$ liquid (unless excessively dilute) to
consist of one or more hydrates. When this liquid is
cooled, the water molecules which coalesce to form soGd
water are derived from these hydrates, the latter becoming
decomposed into other hydrates containing less wkter
and the only portion of the liquid which ads as the
** foreign substance ** is that from which none of the
solvent can be separated by cooling, that is, the sulphuric
acid, and not the 'hydrate. It is the mechanical or
physical effed of these *' foreign '* molecules to which the
lowering of the freezing-point of the solvent must be
mainly attributed in the case of dilute solutions, for ^e
chemical union of the acid and water can have but a
small effed on the result, since the heat absorbed by the
decomposition of a high l^drate into that next below it is
very small in comparison with the heat evolved by the
crystallisation of the water which it gives up (see Proc,
Chtm* Soc,, 1889, p. X49). When there are two dissolved
substances present, the results will be very complicated ;
the acetic acid and the sulphuric acid, for instance, will
each combine with some water in proportions dependent
on their relative affinities for water and on the masses of
each present, and the molecules adine as ** foreign "
molecules and causing the depression will be those water
molecules which are combined by the acetic acid (the
solvent) and the molecules of the hydrate of sulphuric
acid. The case is evidently too complicated for any
dedudsons to be drawn as to the composition of the
latter.

In a case where the substance added to the acetic acid
and water has a much smaller affinity for the water than
the acetic acid has, this latter will , appropriate nearly the
whole of the water, and the other substance will remain
almost anhydrous, or will itself combine with the acetic
acid to form compounds analogous to hydrates. In such
a case the whole of the water (being combined with the
solvent itself), as well as the other substance, ^ill ad as
the *' foreign substance."

This was found to be the case with i^cobol when added
to acetic acid containing water, the depression of the
freexing-point observed being pradically identical with
that which is produced by the alcohol and water when
ading separately. The same was also the case when
water and acetic acid were added to sulphuric acid as a
solvent, the latter, as might have been eipeded, taking
pradically the whole of the water, and the acetic acid
none.

Other results were obtained with calcium chloride and
alcohol, and also with calcium nitrate and alcohol, dissolved
in water. These two salu, which both possess a con-
siderable affinity for alcohol, appear to combine with it»
and depress the freexing-point of water to a smaller
extent than that calculated on the assumption that they
and the alcohol ad independently ; but the diminution of
the depression was not large unless the proportion of salt
added was considerable.

The only conclusion which can be. drawn from these
results is that when two substances possessing a strong
affinity for each other are mixed, there are fewer ading
units present than when they are separate, and that,
therefore, these two substances do not interad so as to
produce dissociation, but combination.



* It must be remarked that, according to the hydrate
tiieory, the present results will not afiord any indication \
of the adual hydrates piesent. When salphuric acid, for
Instance, is dissolved in water, the present hydrate theory

^ For (he exad ttsMiod of calcotation the pnasnt asmber of the
BifitkU mmt bo comiiltod.



ON THB

USE OF AMMONIUM SELENITE FOR THE

DIAGNOSIS OF THE ALKALOIDS.

By A. J. FBRREIRA da 8ILVA.

In a note presented to the Academy in June, X885, Lafon
pointed out a new reagent for morphine and codeine. It
IS ammonium sulphoselenite,- which he prepared by dis-
solving X grm. ammonium selenite in 20 c.c of undiluted
sulphuric acid. This readion gives a green colour with



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Detection and Separation of the Platinum Metals.



f CBBMICALMBirti

• /ont 19, 1891.



the two alkaloids mentioned, but others behave in a
different manner. It is a precious reagent in the tozico-
logical study of poisoning cases by the alkaloids of
opmm.

The author finds that its use may be advantageously
extended for the detedion of some other alkaloids.

He has operated upon the following alkaloids: atro-
pine, aconitme, berberine, brucine, caffeine, cinchonine,
cinchonidine, cocaine, curarine, - delphine, digitaline,
eserine, morphine, narcotine, narceine, papaverine, pilo-
carpine, solanine, saponine, senegine, and veratrioe. The
following results were obtained : —

Atropine,— Ho colouration.

Aconitint.^Ho immediate colouration ; after twenty
minutes a very slight rose-colour.

B#r6tfriii#.— Greenish yellow colour, becoming succes-
sively very brown, rose at the margins, and violet in the
middle ; half-anhour afterwards entirely vinous red,
which lasts for three hours.

Brueine. — Reddish or rose-colour, becoming pale
orange. Half-an-hour after an amber colour, and no
deposit.

Caffiine, — No distinA colouration. At the end of
three hours the liquid was reddish, and there appeared a
very slight deposit, which was not red.

CfiitfAoiftiM.— Nothinp;.

C tiicAont<itfi#.— Nothmg.

Cocaint, — After half-an-hour no decided colouration nor
precipitate. After the lapse of three hours the same
readuon as caffeine.

CiiraWiM.— Slight violet colouration, after some time
reddish. No red deposit at the end of three hours.

Deiphim, — Slightlv reddish colouration passing into a
violet red. No precipitate at the end of three hours.

Digitaliiu, — No immediate colour. Half-an-hour after
the hquid was yellowish. After three hours a reddish
deposit.

£s#rtii#.— Lemon-yellow colour, turning to orange.
Three hours afterwards the colour paler.

Afor^At»#.^Bright greenish blue ; half-an-hour after
marooo-yellow and no deposit. After three hours the
liquid maroon- brown ; no red deposit.

Narcotim.—BXnMh colour, becoming violet and then
reddish. After half-an-hour a fine reddish colour and no
precipitate. After three hours a small red deposit.

NarMfiu.— Yellow-green colour, becoming brownish,
and after half-an-hour reddish. Afterwards a red deposit
at the bottom of the capsule, which is very distind in two
or three hours.

Papavtrine.—BVoXth colour ; the liquid becomes bottle-
green, dirty yellowish green, violet-blue, and then red. A
small bluish deposit at the bottom of the capsule.

Pilocarpine* — Nothing.

So/a»ifitf.~ Canary-yellow, and then brownish. After
halfan-hour a rose-coloured ring. After three hours the
liquid violet-red.

Saj^onin^.— Yellowish, becoming slightly reddish. (Re-
adion not distinA).

Stn§gine,^\Aghx dirty yellow. After three hours
liquid reddish.

Vitatrine, — Indistind yellowish colour, sometimes
with a green tone, after half-an-hour yellow. After three
hours' deposit red and liquid yellowish. (Readion indis-
tind).

Lafon*s reagent thus enables us to distinguish not only
morpheine and codeine, but also berberine, eserine, nar-
cotine, papaverine, solanine, and narceine ; the former by
colour readions ; narceine not only by the immediate
produdion of a yellowish green colour passing into brown
and after half-anhour to reddish, but also by the forma-
tion of a red deposit, which is seen more distindly after
the lapse of two or three hours adhering to the sides, and
the bottom of the capsule.

The author in producing these readions places small



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