ozone and hydrofluoric acid produces none of the reactions described
above.
It is the same with gaseous hydrofluoric acid. Finally we may add that
the hydrofluoric acid employed, as well as the hydrofluorate of
fluoride, were absolutely free from chlorine.
The gas obtained in our experiments is therefore either fluorine or a
perfluoride of hydrogen.
New experiments are necessary to settle this last point. We hope soon
to lay the results before the Academy.--_Comptes Mendus_, vol. ciii.,
p. 202, July 19, 1886; _Chem. News._
* * * * *
COHESION AND COHESION FIGURES.[1]
[Footnote 1: Notes from a lecture given to the Halifax Scientific
Society, July 19, 1886.]
By WILLIAM ACKROYD, F.I.C.
_1. A Law of Solubility._
It is customary to regard cohesion as the force which binds together
molecules of the same substance, and in virtue of which the particles
of solids and liquids are kept together, and also to speak of the
attraction exerted between particles of two different bodies as
adhesion. The distinction between cohesion and adhesion is a
conventional one. The similarity, if not identity, of the two forces
is demonstrated by the fact that while cohesion is exerted between
particles of the _same_ body, adhesion is exerted with most force
between particles of _allied_ bodies. Generally speaking, organic
bodies require organic solvents; inorganic bodies, inorganic solvents.
For example, common salt is highly soluble in water, but not in ether,
and many fats are soluble in ether, but not in water. So many cases
like these will suggest themselves to the chemist that I am justified
in making the following generalization: _A body will dissolve in a
solvent to which it is allied more readily than in one to which it in
highly dissimilar._ Exceptions to the law undoubtedly exist, but none
so striking as the following in support of it, viz., that the metal
mercury is the only known true solvent for many metals at the normal
temperature.
_2. Its Connection with Mendeleeff's Periodic Law._
From this standpoint the whole subject of solution is deserving of
fresh attention, as it appears highly probable that, just as Prof.
Carnelley has shown by the use of my meta-chromatic scale, the colors
of chemical compounds come under definite laws, which he has
discovered and formulated in connection with Mendeleeff and Newlaud's
periodic law,[2] so, likewise, may the solubility of an allied group
of compounds, in regard to any given solvent under constant conditions
of temperature, conform to similar laws; that, e.g., the chlorides
of H, Na, Cu, and Ag, in Mendeleeff's Group I., may vary in their
solubility in water from an extreme of high solubility in the case of
hydrogen chloride to the opposite extreme of comparative insolubility
in the case of silver chloride. In this natural series of compounds,
hydrogen chloride is the body nearest akin to water, and silver
chloride the most remote in kinship.
[Footnote 2: _Philosophical Magazine_, August, 1884.]
_3. A Solidified Vortex Ring._
It is in virtue of cohesion that a freely suspended drop of liquid
assumes the spherical form. If such a sphere be dropped on to the
surface of a liquid of higher specific gravity at rest, one obtains
what is called the cohesion figure of the substance of the drop. A
drop of oil, e.g., spreads out on the surface of water until it is a
circular thin film of concentric rings of different degrees of
thickness, each displaying the characteristic colors of thin plates.
The tenuity of the film increases; its cohesion is overcome; lakelets
are formed, and they merge into each other. The disintegrated portions
of the film now thicken, the colors vanish, and only islets of oil
remain. Some liquid drops of the same or higher sp. gr. than water do
not spread out in this fashion, but descend below the surface of the
liquid, and, in descending, assume a ring shape, which gradually
spreads out and breaks up into lesser rings. Such figures have been
termed submergence cohesion figures; they are vortex rings. I have
solidified such vortex rings in their first stage of formation. If
drops of melted sulphur, at a temperature above that of the viscous
state, be let fall into water, the drops will be solidified in the
effort to form the ring, and the circular button, thick in the rim and
thin in the center, may be regarded as a solidified vortex ring of
plastic sulphur.
_4. That a Submergence Cohesion Figure is a Vortex Ring._
It may be shown that the conditions of the formation of a submergence
cohesion figure are those which exist in the formation of an aerial
vortex. Those conditions in their greatest perfection are (1) a
spherical envelope of a different nature from the medium in which the
rings are produced; (2) a circular orifice opening into the medium;
and (3) a percussive impact on the part of the sphere opposite the
orifice. In the production of vortex rings of phosphorus pentoxide in
the making of phosphoreted hydrogen, the spherical envelope is water,
the orifice the portion of the bubble which opens into the air
immediately it rises to the surface, and the impact is furnished by
gravity. So, also, in the case of a submergence cohesion figure, the
spherical envelope is the air surrounding the drop, the orifice the
portion of it which first comes in contact with the liquid at rest;
and here again the impact is due to gravity more directly than in the
former case. These conditions are somewhat imperfectly copied in the
ordinary vortex box, which is usually cubical in form, with a circular
orifice in one side, and a covering of canvas on the opposite one,
which is hit with the fist.
* * * * *
[AMERICAN CHEMICAL JOURNAL.]
THE DETERMINATION OF NITRIC ACID BY THE ABSORPTION OF NITRIC OXIDE
IN A STANDARD SOLUTION OF PERMANGANATE OF POTASSIUM.
By H.N. MORSE and A.F. LINN.
The method which we propose consists in the conversion of the nitric
acid into nitric oxide; the absorption of the latter in a measured,
but excessive, quantity of a standard solution of permanganate of
potassium; and the subsequent determination of the excess of the
permanganate by means of a standard solution of oxalic acid or
sulphate of manganese.
THE APPARATUS.
A is an apparatus for the generation of carbon dioxide free from air,
which will be explained hereafter.
B is a flask, having a capacity of 125 or 150 c.c., in which the
nitrate is decomposed in the usual manner by means of ferrous chloride
and hydrochloric acid.
C is a small tube for the condensation of the aqueous hydrochloric
acid which distills over from B.
D is a Geissler bulb, containing a concentrated solution of potassium
carbonate, to arrest any acid vapors coming from C.
E, E are two pieces of ordinary combustion tubing, having a length of
about 650 or 700 mm., in which is placed the permanganate solution
employed for the absorption of the nitric oxide. Their open ends are
provided with lips in order to facilitate the pouring of liquids from
them, care being taken not to so distort the ends that rubber stoppers
cannot be made to fit them tightly. They are placed in a nearly
horizontal position in order to diminish the pressure required to
force the gases through the apparatus and thus lessen the danger of
leakage through the rubber joints.
_a_ is a tube through which the ferrous chloride and hydrochloric acid
are introduced into B, as in the method of Tiemann-Schulze.
_b_ serves for the introduction of carbon dioxide to expel the air
before the decomposition of the nitrate, and the nitric oxide
afterward.
_c_ is an unbroken tube ending at the lower surface of the stopper in
B, and at the bottom of C.
The rubber joint, _d_, is furnished with a Mohr and also a screw pinch
cock. The joints, _e_ and _f_, are furnished with Mohr pinch cocks.
The rubber tubing upon these should be of the best quality, and must
be carefully tied.
[Illustration: DETERMINATION OF NITRIC ACID.]
THE SOLUTIONS.
In consequence of the large volume of the permanganate solution
required for the complete absorption of the nitric oxide, we have
found it advantageous to use three solutions instead of two.
1. A solution of permanganate such that one c.c. is equivalent to
about fifteen milligrammes of nitrate of potassium, according to the
reaction:
KMnO_{4} + NO = KNO_{3} + MnO_{2}.
This solution is employed for the absorption of the nitric oxide. Its
strength need not be exactly known. There is no objection to a more
concentrated solution, except that which pertains to all strong
standard solutions, namely, that a small error in measurement would
then give a larger error in the results. 100 c.c. of this solution are
required for each determination, and the measurement is always made in
one and the same 100 c.c. measuring flask, which, if necessary, should
be labeled to distinguish it from that used for solution No. 2.
2. A solution of oxalic acid which is very slightly stronger than that
of the permanganate just described--that is, a solution such that one
c.c. of it will somewhat more than decompose one c.c. of the
permanganate, according to the reaction:
2KMnO_{4} + 3H_{2}SO_{4} + 5C_{2}H_{2}O_{4}.2H_{2}O =
K_{2}SO_{4} + 2MnSO_{4} + 18H_{2}O + 10CO_{2}.
The exact strength of this solution need not be known, since we only
require the difference in value between it and solution No. 1, which
is determined by means of solution No. 3. 100 c.c. of this solution
are also required for each determination, and the measurement, as in
the preceding case, is always made in the same 100 c.c. measuring
flask.
3. A dilute, carefully standardized solution of permanganate of
potassium.
The method of using these solutions is as follows: 100 c.c. of No. 1
and No. 2 are measured off (each solution in its own measuring flask),
brought together in a covered beaker glass, and acidified with dilute
sulphuric acid. The excess of oxalic acid is then determined by means
of solution No. 3.
When it is desired to make a determination of nitric acid, 100 c.c. of
solution No. 1 are measured off, and as much of it as may be
convenient is poured into the tubes, E, E, together with about a
gramme of zinc sulphate for each tube, which substance appears to
considerably facilitate the absorption of the nitric oxide by the
permanganate. When the operation is over, the contents of E, E are
poured into a beaker glass. 100 c.c. of solution No. 2 are then
measured off, and a portion, together with a little sulphuric acid,
poured into E, E, to dissolve the oxide of manganese which has
separated during the absorption of the nitric oxide. The oxide having
been dissolved, the liquid in E, E, and the rinsings of the tubes,
also the residues of permanganate and oxalic acid left in the
measuring flasks, and the rinsings from these, are all brought
together in the same beaker glass. Finally, the amount of solution
No. 3 required to decompose the excess of oxalic acid is determined.
If we subtract from the amount thus found the quantity of permanganate
required to equalize solutions Nos. 1 and 2 (previously ascertained),
we shall have the amount of permanganate actually reduced by the
nitric oxide, according to the reaction:
6KMnO_{4} + 10NO = 3K_{2}O + 6MnO + 5N_{2}O_{5};
in other words, on the basis that one molecule of potassium
permanganate will oxidize one and two-thirds molecules of nitric
oxide:
(KMnO_{4} = 1-2/3 NO).
The method of using the apparatus is simple. The nitrate is placed in
B, and the joints made tight, except that at _f_, which is left open.
A current of carbon dioxide is passed through the apparatus until all
of the air has been displaced. Connection is then made at _f_, and
soon afterward the current of carbon dioxide is shut off at _d_.
The flask, B, is now heated as long as may be necessary in order to
produce, on cooling, the diminished pressure required for the
introduction of the ferrous chloride and hydrochloric acid. Before
removing the flame, the joint at _f_ is closed to prevent the return
of the permanganate solution.
As soon as the flask, B, has become sufficiently cool, the ferrous
chloride and hydrochloric acid are introduced through the tube, _a_
(which has been full of water from the first), in the same manner and
quantities as in the well-known Tiemann-Schulze method.
The pinch cock at _d_ is then opened, and the apparatus allowed to
fill with carbon dioxide. When the pressure has become sufficient to
force the gas through the solution of permanganate, the pinch cock at
_f_ is removed. It should be opened only slightly and with great
caution at first, unless one is certain that the pressure is
sufficient. If the pressure is insufficient, the fact will be made
apparent by a rise of the permanganate in the small internal tube.
The flow of carbon dioxide is now reduced to a very slow current, or
entirely cut off. The contents of B are slowly heated, until the
decomposition of the nitrate is complete and the greater part of the
nitric oxide has been expelled, when the apparatus is again closed at
_f_ and _d_, and allowed to cool. The tube, _a_, is then washed out,
by the introduction through it into B of a few cubic centimeters of
strong hydrochloric acid.
The process of filling the apparatus with carbon dioxide, and of
heating the contents of B, is repeated. When it becomes apparent, from
the light color of the liquid in B, that all of the nitric oxide has
been expelled from it, the current of carbon dioxide is increased and
the heating discontinued. Care must be taken, however, not to admit
too strong a current of carbon dioxide, lest some of the nitric oxide
should be forced unabsorbed through the permanganate solution. It is
also necessary, for the same reason, to avoid too rapid heating during
the decomposition of the nitrate.
When all of the nitric oxide has been forced into the solution of
permanganate, the determination is made in the manner already
described.
To test the method, nine determinations were made with quantities of
pure nitrate of potassium varying from 100 to 200 milligrammes. The
maximum difference between the volumes of permanganate actually used
and those calculated was 0.05 c.c., while the main difference was
0.036 c.c. The measurements of the permanganate were made from a
burette which had been carefully calibrated. We also made a number of
determinations, using a solution of manganous sulphate in the place of
the oxalic acid. The advantage of this method lies in the fact that it
is not necessary to dissolve the oxide which is precipitated upon the
glass within the tubes, E, E, since, in the presence of an excess of
permanganate, the reduction by nitric oxide extends only to the
formation of MnO_{2}; also in the fact that the solution of manganous
sulphate is more stable than that of oxalic acid. A solution of the
sulphate having been once carefully standardized, can be used for a
long time to determine the value of permanganate solutions.
The details of the method are as follows: A solution of manganous
sulphate slightly stronger than No. 1 is prepared.
The difference between 100 c.c. of it and 100 c.c. of No. 1 is
ascertained, according to the method of Volhard, by means of solution
No. 3.
The contents of E, E, together with the rinsings from the tubes, are
poured into a capacious flask. 100 c.c. of the manganous sulphate and
a few drops of nitric acid are then added, and the whole boiled.
Finally, the excess of manganous sulphate is determined, in the manner
described by Volhard, by means of solution No. 3. Subtracting from the
total amount of permanganate thus used the quantity required to
equalize the 100 c.c. of solution No. 1 and the 100 c.c. of the
manganous sulphate, we shall have the quantity of permanganate reduced
by the nitric oxide.
It must, however, be remembered that the value of solution No. 3 is
now to be calculated on the basis of the equation KMnO_{2} + NO =
KNO_{3} + MnO_{2}. One molecule of permanganate equals one molecule of
nitric oxide when manganous sulphate is used, since no part of the
permanganate employed in this method is reduced below the superoxide
condition. In other words, solution No. 3 now represents only
three-fifths as much nitric acid as it does when oxalic acid is used.
The results obtained by this method were moderately satisfactory, but
not quite so exact as those obtained when oxalic acid was used. A
series of four determinations gave differences, between the volumes of
permanganate calculated and used, of 0.05 to 0.15 c.c.
The principal objection to the method lies in the difficulty of
determining, in the presence of the brown oxide of manganese, the
exact point at which the oxidation is complete.
The carbon dioxide generator, A, was devised by us to take the place
of the ordinary generators, in which marble is used. We have found
that a submersion of twenty hours in boiling water does not suffice to
completely remove the air which, as is well known, is contained in
ordinary marble; hence some other substance must be employed as a
source of the gas. In the apparatus which we are about to describe,
the acid carbonate of sodium is used.
It consists of a long, narrow cylinder (450 x 60 mm.); a tightly
fitting rubber stopper, through which three tubes pass, as shown in
the figure; a small cylinder, F, containing mercury; and a sulphuric
acid reservoir, G.
The tube, _g_, is drawn out to a fine point at the end and curved, so
that the acid which is delivered into A falls upon and runs down the
outside of the tube. The tube, h, dips under the mercury in F. G and
_g_ are connected by means of a long piece of rubber tubing which is
supplied with a screw pinch cock.
The apparatus is made to give any required pressure by raising or
lowering G and F; but the elevation of G, as compared with that of F,
should always be such that the gas will force its way through h rather
than g. The upper part of the cylinder, F, is filled with cotton wool
to prevent loss of mercury by spattering.
The material placed in A consists of a saturated solution of acid
carbonate of sodium, to which an excess of the solid salt has been
added. The sulphuric acid is the ordinary dilute. The apparatus, if
properly regulated, serves its purpose very well. The principal
precaution to be observed in using it is to avoid a too sudden
relieving of the pressure, which would, of course, result in the
introduction of an unnecessarily large quantity of sulphuric acid into
A.
* * * * *
WATER OF CRYSTALLIZATION.
By W.W.J. NICOL, M.A., D.Sc.
When a hydrated salt is dissolved, does it retain its water of
crystallization, or does this latter cease to be distinguishable from
the solvent water? Both views have found advocates among chemists who
have looked at the question of solution, and both have been supported
by arguments more or less to the point. But among the possible means
of solving this question there is one which has entirely escaped the
notice of those interested in the subject. And those who hold that
water of crystallization exists in solution have been entirely
oblivious of the fact that, while they are ready to accept the results
of the modern science of thermo-chemistry, and to employ them to
support their views on hydration, yet these very results, if correct,
prove without a shadow of a doubt that water of crystallization does
not exist in solution.
The proof is so clear and self-evident when once one's attention is
directed to it, that, though I intend to develop it more fully on
another occasion, I feel that it is better to publish an outline of it
at once.
Thomsen has found that the heat of neutralization of the soluble bases
of the alkalies and alkaline earths with sulphuric acid has a mean
value of 31.150 c. within very narrow limits. When hydrochloric or
nitric acid is employed, the value is 27.640 c., also within very
narrow limits. Now, this agreement of the six bases in their behavior
with sulphuric acid, much more of the seven bases with both HNO_{3}
and HCl, is so close that it cannot be regarded as accidental, but, in
the words of Meyer, the heat of formation of a salt in aqueous
solution is a quantity made up of two parts, one a constant for the
base, the other for the acid. But of the twenty salts thus formed,
some are anhydrous in the solid state, others have water of
crystallization, up to ten molecules in the case of Na_{2}SO_{4}. If
water of crystallization exists in solution, it will be necessary to
suppose that this agreement is accidental, which is absurd, as a
glance at the probabilities will show. Thomsen himself expressly
states that he regards the dissolved state as one in which the
conditions are comparable for all substances; this would be impossible
if water of crystallization were present.
A still stronger proof is afforded by the "_avidity_" of Thomsen or
the "_affinity_" of Ostwald; both have worked on the subject, taking
no account of water of crystallization, and the results, e.g., for
H_{2}SO_{4} and HCl with NaHO, where water of crystallization _may_
come in, are entirely confirmed by Ostwald's results on inversion and
etherification, where there can be no water of crystallization.
The proof is complete, water of crystallization cannot be attached to
the salt in solution, or if it is, no heat is evolved on union more
than with solvent water. The alternative is to suppose that the whole
of the above thermo-chemical results are coincidences.
* * * * *
ALPINE FLOWERS IN THE PYRENEES.
Bagneres De Luchon, in the department of the Haute Garonne, is a gay
town of some 5,000 inhabitants. A friend told me that he once suffered
so much from the heat there in June, that he determined never to go to
the Pyrenees again. We were there the second week in June, and we
suffered more from rain and cold, and were very glad of a fire in the
evening.
Except to the south, in the direction of the Porte de Venasque, one of
the chief mule passes into Spain during summer, where there are fine
snow-capped mountains, the scenery from the town is not grand, but it
is within easy reach of the wildest parts of the Pyrenees.
It is the nearest town to the Maladetta, their highest point, in which
the Garonne rises, and among whose rocks is one of the last
strongholds of the ibex or bouquetin, the "wild goat" mentioned by
Homer. Eagles and vultures are to be seen sailing about the sky near
Luchon nearly every day, and bears, which in the Pyrenees are neither
mythical nor formidable, descend to within a few miles of the town
after wild strawberries, which abound there.
We heard of two female peasants lately gathering wild strawberries who
were suddenly confronted with competitors for the spoil in the shape
of a she bear and two cubs. It was doubtful whether man or beast was
the more surprised. The cubs began to growl, but their dam gave both
of them a box on the ears for their bad manners, and led them away. As
for flowers, the neighborhood of Luchon has the reputation, perhaps
not undeserved, of being the most flowery part of the Pyrenees.
We went the usual expeditions from the town, in spite of the weather,
and I will try to remember what plants we noticed in each of them. The
first trip was to the Vallee du Lys. In spite of the spelling, the
name suggests lilies of the valley, but we are told that lys is an old
word meaning water, and that the valley took its name from the number
of cataracts, not from lilies, there.
However this may be, a lily grows there in great profusion, and was
just coming into flower toward the middle of June. It is the Lis de
St. Bruno (Anthericum liliastrum), a plant worthy of giving its name
to a valley of which it is a characteristic feature. Still more
conspicuous at the time when we were there were the Narcissus
poeticus, abundant all round Luchon, but already past in the low
meadows near the town, but higher up, at an elevation of about 4,000
ft., it was quite at its best, and whitened the ground over many
acres.