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By Weight. By Volume.

H 2 = 2 = 2

= 16 = 1



H 2 = 18 = 2

Water would therefore be a suboxide of hydrogen, while the peroxide would
become the oxide (HO). Protoxide of nitrogen would in like manner be a
suboxide N a O, and the deutoxide would become the protoxide (NO). la
respect to this theoretical constitution, it may be remarked that the chemical
properties of water are really those of a neutral oxide, and not of a suboxide.
Faraday considers that the electrolysis of water proves it to be a protoxide,
i. e., a compound of one atom of each element, HO. On the other hand, the
peroxide of hydrogen represented by the unitary system as a neutral oxide,



72 . THE UNITARY SYSTEM OF NOTATION.

HO, has none of the characters of a neutral oxide ; but from the facility with
which it parts with half of its oxygen, it more strikingly resembles a peroxide,

H0 2 .

The compounds of hydrogen and nitrogen with oxygen serve to illustrate
the inconsistency of the new system of nomenclature. Thus N 2 is described
as nitrous oxide, but H 3 is described by the same authority as hydric oxide,
or oxide of hydrogen. Again, NO is represented as nitric oxide, while HO
stands as hydric peroxide, or peroxide of hydrogen. It is clear that if this
view is correct, that the compounds are respectively on the unitary system
suboxides and oxides, and water should be aqueous oxide, and oxywater
hydric oxide. This should be the true nomenclature, if the old names of
nitrous and nitric oxide have been properly applied to the analogous com-
pounds of nitrogen with oxygen.

It is stated in favor of this method, that it is better adapted for expressing
the formula of certain organic compounds than that now in use ; and that,
in reference to compound gases and vapors, the atoms may be so arranged
that they will all yield two volumes the specific gravities of the compounds,
compared with hydrogen, being then equal to one-half of their atomic weights.
Thus carbonic oxide C O forms 2 volumes of gas (the atoms being doubled) ;
the atomic weight is 12-f 16, or 28, and the specific gravity, compared with
hydrogen, equal to one-half, or 13.95. Alcohol is C a H (i O ; it forms 2 volumes
of vapor; the atomic weight is 24 + 6-J-16 46, and the specific gravity,
compared with hydrogen, is one-half of this, namely, 23. Chemical facts
are, however, somewhat strained to suit the requirements of this hypothesis.
The specific gravities of arsenic and phosphorus in vapor, compared with
hydrogen, are double their atomic weights, being 152.79 and 63.71 respect-
ively. The atomic weights (75 and 32) therefore represent only half a
volume instead of one volume of each element ; and one volume of arsenic
or phosphorus must represent two atoms. Either, therefore, the system is
inconsistent with itself, and the assumption that the volume of an element
represents one atom, or its atomic weight, is contrary to known facts or,
in order to bring arsenic and phosphorus within the rule, the atomic weights
of these elements must be doubled on this system of notation. So with sul-
phur the atomic weight being 32, the specific gravity of the vapor, com-
pared with hydrogen, is 3 times this weight, or 96. Hence, instead of an
atom of sulphur corresponding to one volume, it would be represented by ^
of a volume. By ingeniously selecting a specific gravity of sulphur-vapor
calculated for the unusual temperature of 1900, in place of the ordinary
specific gravity at 900, this element is made apparently to fall within the
rule. Oxygen itself only falls within it by doubling the equivalents of all
the bodies with which this element combines.

This system, therefore, introduces duplicate or molecular atoms in place of
the usual single atoms. Elements are supposed to enter into combination
with themselves before they can enter into combination with other elements.
Thus hydrogen does not exist in all cases as H, but on some occasions as
HH or H a ; in other words, it is supposed to form a compound of itself, or
a hydride of hydrogen, and nitrogen is also NN, or a nitride of nitrogen. We
have here not only a departure from simplicity, but from all analogy. Thus

we are told that anhydrous oxide of potassium is ^ [ 0, while the anhydrous

chloride, bromide, iodide, and fluoride, would be represented by one atom of
each, KC1 or KBr, &c. The analogy of composition between oxide and
chloride is thus set aside : and the names of compounds are no longer in
accordance with their chemical constitution. The present language has been



NOMENCLATURE OF SALTS. 73

found adequate to explain all chemical changes that are of any importance
and require explanation ; and although in some respects imperfect, it has
this great advantage, that it has taken a deep root not only in the arts and
manufactures of this country, but in medicine and pharmacy.

Nomenclature. Constitution of Salts. Elementary bodies often take their
names from their peculiar physical properties as chlorine and iodine in refer-
ence to color, and bromine to odor : in some instances the name is derived
from the products of combination, as oxygen, hydrogen, nitrogen, and cyano-
gen. The general principle of nomenclature as applied to compounds, has
been, as far as possible, to indicate the composition of the substance by the
name. Thus sulphate of potash implies at once the constitution of this salt :
it was formerly called the sal de duobus. Its formula is KO,S0 3 , and herein
its composition is at once announced. The same observation applies to other
salts. In regard to the common metals, the salts receive the name of the
metal, as sulphate of copper CuO,S0 3 . The acid, however, as in the case of
sulphate of potash, is believed to be combined with oxide of copper, and not
with the metal itself. Among the alkalies the oxides were known long before
the metals, and received specific names, which have been since retained. In
recent times it has been proposed to assimilate the names of metallic salts,
by using a common designation. Thus the sulphate of potash is described
as sulphate of potassium, on the hypothesis that the acids are not combined
directly with the oxides, but with the metals. If, as we believe, this hypo-
thesis is inconsistent with chemical facts, then a retrograde step in nomencla-
ture has been taken, since a name which suggests a direct combination of an
acid or acid radical with a metal, conveys no incorrect idea of the constitu-
tion of salts.

A salt is a compound of an acid and a base. An acid is a compound which
has an acid or sour taste, which reddens the blue color of litmus, and neu-
tralizes an alkali in combining with it to form a salt. But according to some
modern chemists, an acid is a salt, and all acids are described as salts of
hydrogen. There are some acids, however, which neutralize alkalies or bases
and form definite salts, but they form no compound with water and are never
found associated with hydrogen in any form. Thus hyponitrous acid (^S0 3 )
forms a well-known class of salts, the hyponitrites of the alkaline and
metallic oxides. When water is added to the anhydrous acid, this acid is
immediately decomposed. It is the same with hyponitric (nitrousj acid N0 4 .
It forms however well-defined nitro-compounds with cellulose, glycerine, and
benzole. It performs all the functions of an acid, but when water is placed
in contact wi^h it, it undergoes decomposition. It enters into no combina-
tion with the elements of water. It is, therefore, impossible to describe an acid
as a salt of hydrogen, except by ignoring the existence of a large class of
substances which have all the characters of acid, except the power of combining
with water or its elements. Even some which combine with water as a
solvent, such as the carbonic and sulphurous acid gases, form no hydrates
or chemical compounds with water. They may be obtained perfectly free
from water or its elements but they combine with metallic oxides and pro-
duce well-known crystalline salts. Among solids the fused boracic and
silicic acids form a large number of saline compounds by uniting as acids to
bases, wholly irrespective of the presence of water.

The term base is applied by chemists to signify a compound which will
chemically combine with an acid : it includes alkalies (oxides of alkaline
metals, and alkalies of the organic kingdom), oxides of the ordinary metals,
and a variety of complex compounds in the organic kingdom which are not
alkaline and possess none of the characters of metallic oxides. The metals
which form bases are are now called basylous bodies. An alkali is known



74 NOMENCLATURE OF SALTS.

by its having an acrid or caustic taste, by its rendering a red solution of
litmus blue, and by its being neutralized by an acid, i. e., having its alkaline
properties entirely destroyed. Further, it has the property of turning yellow
turmeric to a red-brown color ; the red color of the petals of flowers, and
fruits, to a blue or green ; and the red color of woods and roots to a crim-
son tint. The basic metallic oxides are generally insoluble in water, and
neutral to test-paper ; some have a feebly alkaline reaction.

In reference to Oxacids, or those which contain oxygen, the termination
ic indicates the higher degree of oxidation, while the termination ous im-
plies a lower degree. Thus we have sulphuric (SO,,) sulphurous (S0 3 ) acids.
When there are more than two acids, a further distinction is made by the
prefix hypo (vrtb under) : thus we have hyposulphuric acid to signify an acid
containing a smaller quantity of oxygen than the sulphuric, but a larger quan-
tity than the sulphurous ; and hyposulphurous, indicating a smaller quantity of
oxygen than exists in the sulphurous acid. When an acid has been discovered
containing a still larger amount of oxygen than the highest in a known series,
it receives the prefix hyper (vrtep above) ; still retaining the terminal ic.
Thus there is manganic acid (Mn0 3 ) ; and hypermanganic or permanganic
acid (Mn 2 7 ), which contains a still larger proportion of oxygen than the
manganic. The salts formed by these acids terminate in ate when the acid
terminates in ic, and in ite when it terminates in ous. The terminations
ic and ous have been employed by Berzelius, and other chemists, to dis-
tinguish the oxides and salts of metals. Thus the protoxide of iron would
be the ferrous oxide, while the peroxide would be the ferric oxide ; so there
are also ferrous and ferric sulphates stannous and stannic chlorides and
sulphides.

When there is only one acid formed by the same elements, its termina-
tion is always in ic, as the boracic acid, formed of boron and oxygen, of
which only one compound is known. The class of hydracids includes those
binary compounds in which hydrogen is a constituent ; and the names imply
at once the composition as hydrochloric acid (HC1). Hydrogen, unlike
oxygen, does not form more than one compound with the same element or
radical. These hydrogen acids require no water for the manifestation of
acidity. The term radical, or compound radical, is applied to a compound
which in its order of combination acts like an element. Thus the compound
gas cyanogqji (NC a ) is a radical ; it enters into combination with the metals
and metalloids, like chlorine, producing binary compounds called cyanides.
It is a substitute for an element.

When in the composition of salts the atoms of acids preponderate, the
prefix bi or ter is used to indicate the number, as bisulphate of potash
(K02SO,), or tersulphate of alumina (A1 3 O 3 3S0 3 ). These constitute acid
salts. When the base predominates, the abbreviated Greek prefix di or tri
is employed to designate the surplus atoms of the base. Thus, the triacetate
of lead signifies a compound in_ which three atoms of oxide of lead are united
to one atom of acid 3PbO,Ac. The terra sesqui is used to signify one and
a half atoms, or avoiding fractions, 3 atoms of base to 2 of acid, as 3PbO,2Ac.
The following Table represents the nomenclature cf salts in reference to their
constitution. M stands for any metal :

Neutral (normal) salt MO-J- S0 3 Bibasic .... 2MO-f- S0 3

A cid MO-f2S0 3 Sesquibasic . . . 3MO+2S0 3

Sesquisalt .... 2MO-|-3S0 3 Tribasic .... 3MO-J- S0 3

Binary Compounds. The Binary System. When a metalloid is united to
another metalloid or metal, or when a compound radical (salt-radical) is



ON THE CONSTITUTION OF SALTS. 75

united to a metal or metalloid, the combination is called binary, from its
consisting of two elements. They are generally known by the termination
ide. Thus oxide, chloride, sulphide, carbide, phosphide, and cyanide indicate
compounds of the elements or of the radical (cyanogen) with other elements.
When more than one combination exists, the compounds take the Greek prefix
proto, deuto, trito, or di, to indicate the respective number of atoms of the
constituents. (See OXYGEN for the series of Oxides.} The highest combi-
nation always takes the prefix/?er. The binary compounds formed by chlorine,
bromine, iodine, and fluorine, with the alkaline metals, are frequently called
haloid salts, to indicate the marine origin of the radicals (a*.?, ax6j, the sea).
Chloride of sodium furnishes an instance of a binary compound ; and as
nitrate of silver or nitrate of potash equally forms a salt bearing a physical
resemblance to the chloride, it has been suggested that in oxacid salts the
elements may be so arranged as to form hypothetical binary compounds.
Chloride of sodium is NaCl and nitrate of silver is AgO,N0 5 ; but the
accepted symbolic language would admit of the atomic arrangement AgNO 6 ,
and by this means all decompositions would become mere substitutions of
one metal for another, or for hydrogen. Thus in the production of chloride
of silver we should have in ordinary symbols NaCl4-AgO,N0 5 =AgCl-j-
NaO,N0 5 ; but if the oxygen is supposed to be associated with the elements
of nitric acid, forming a compound radical (nitron), then the changes would
be more simply represented thus: NaCl-f AgNO(.=AgCl-{-NaN0 6 . If, how-
ever, this view were correct, it should apply to all salts and even to hydrates.
Thus, to take a few examples of compounds which are intelligibly represented
by the present method, we should have, on the binary hypothesis, to make
the following changes : 1. Carbonate of soda, as a type of the carbonates,
NaO,CO 3 would be rendered Na,C0 3 ; and for the bicarbonate of soda,
NaO,2CO d a new hypothetical radical would have to be created, as Na,C 3 5
or Na,C0 3 -fC0 2 , neither of which formulae would convey the slightest know-
ledge of the composition of the salts. This objection equally applies to all
salts having one atom of base to two or more atoms of acid, as the bisul-
phates, bisulphites, the binarsenates, and others, as well as to all double
salts containing an oxygen acid. 2. In the application of this notation to
hydrates (which could not be fairly expected), hydrate of potash KO,HO
would be K,H0 2 ; but while potassium (K) has a stronger affinity for oxygen
than any other known substance, and peroxide of hydrogen (H0 2 ) so readily
parts with oxygen that the mere contact with metals or metallic oxides is
sufficient for the purpose, it is assumed that the peroxide can remain in com-
bination with potassium without undergoing decomposition. 3. Sulphurous
acid by combining with potash forms KO,S0 3 . It could not be regarded or
written as KS0 3 , for this would imply a combination of anhydrous sulphuric
acid with the metal potassium. The bisulphate of potash KO,2S0 3 , would
present an equal difficulty. On the binary system this would be K,S a O ft
the sulphur and oxygen, in order to form a salt radical, being here associated
as in hyposulphuric acid, which is a well-known and independent acid of sul-
phur. 4. The anhydrous salts formed of metallic bases and acids could not
be consistently represented on the binary hypothesis ; for there could be no
definite principle on which the oxygen should be wholly assigned to either
metal. Thus chroraate of lead is commonly represented as PbO,Cr0 3 , but
as a binary compound it would be either Pb,Cr0 4 , or CrPb0 4 . Of these
three combinations of elements, those only which are known and separable,
are oxide of lead and chromic acid. The necessary creation of an endless
number of hypothetical radicals, some already conflicting with known com-
pounds, is indeed fatal to the hypothesis. It would add complexity instead
of simplicity to chemical formula. While N0 3 , S0 3 and C0 2 have a real



76 NEUTRALIZATION AND SATURATION.

and independent existence, the binary radicals N0 6 , S0 4 and C0 3 are mere
assumptions. It has been supposed that the electrolytic decomposition of
salts is in favor of this view ; but although the metal may be separated from
the salt by an electric current, the supposed binary radical has never been
obtained, and the facts are fully explained on the supposition that it is
S0 3 -fO, and not S0 4 . On the other hand, ordinary electrolysis favors the
common view of the constitution of salts by acid and base, as the following
simple experiment will show. Provide a piece of glass tube, bent at an angle,
and placed in a wine-glass, to serve for its foot or support. Fill this siphon
with the blue infusion obtained by macerating the leaves of the red cabbage
in boiling water (rendered blue by a little potash), and put into it a few
crystals of sulphate of soda ; then place a strip of platinum foil in each leg
of the siphon, taking care that they do not come into contact at the elbow
of the tube, and connect one of these with the negative and the other with
the positive pole of the pile; in a few minutes the blue color will be changed
to green on the negative side, and to red on the positive side of the tube,
indicating the decomposition of the salt, the alkali or soda of which is col-
lected in the negative, and the sulphuric acid in the positive side. Reverse
the poles, and the colors will also gradually be reversed. In this and ana-
logous experiments, it is found that, whenever a neutral salt is decomposed
by electricity, the oxide or base appears at the cathode, and the acid at the
anode. The bases, therefore, in their electrical relations, rank with hydro-
gen, and are cathions ; and the acids with oxygen, and are anions (see page
59) : The least soluble salts may be made to render up their elements m
the same way. If, for instance, we substitute for the sulphate of soda in
the preceding experiment, a little finely-powdered sulphate of baryta
moistened with water, baryta will be evolved at the cathode, and will there
render the liquid green ; while sulphuric acid will appear at the anode, ren-
dering it red.

If the binary hypothesis were adopted, it would be necessary to change
the names of all salts. C0 3 is not carbonic acid ; it would be necessary to
invent a new term for this radical, to indicate its composition, e. g., a teroxy-
carbide, so that dry carbonate of potash KO,C0 2 , would be a teroxycarbide
of potassium KC0 3 . If names are not to express, as far as may be, the
composition of salts, it would be 'preferable to return to the old nomencla-
ture based on physical properties, and to designate the sulphate of iron
(FeO,S0 3 ) as green vitrol, rather than under the binary hypothesis as the
tessaroxisulphide of iron (FeS0 4 ). We must bear in mind, in reference to
such changes, that the supposed advantages gained in one part of the science
may be far more than counterbalanced by the disadvantage of using names
which either do not express the nature of the compound, or which express it
in such formulas as to deceive the student of the science. As Dr. Miller has
pointed out, there are four ways in which nitrate of potash may be repre-
sented ; KO,N0 5 ; K,N0 6 ; KN0 6 ; and KN0 3 ; but to only the first of
these is the usual name of the salt applicable. The first, second, and third
formula are on the ordinary system of notation ; the fourth is on the system
of Gerhardt, which, except by some conventional understanding, cannot
represent the presence of potash or nitric acid in the salt on any reasonable
interpretation.

There are some cases in which the binary theory of salts is inadmissible
not only with respect to oxacids, but to hydracids. The alkalies of the
vegetable kingdom form definite crystallizable salts with the hydrochloric,
sulphuric, and nitric acids. The hydrochlorate and sulphate of morphia
are well-defined salts, in which there is every reason to believe that acid and
base are directly combined. Even in the mineral kingdom, there is some-



DECOMPOSITION OF NEUTRAL SALTS. 77

times a want of evidence of this binary condition. Magnesia or alumina
may be dissolved in hydrochloric acid, and it is supposed that soluble
chlorides are formed. In the case of soda and potash there is the strongest
evidence of the production of chlorides by the (act that the binary salts are
obtainable as such by crystallization. On submitting to evaporation the
hydrochloric solutions of magnesia and alumina and applying heat to the dry
residues, no binary compounds are obtained, but simply the bases which
were originally employed. According to some authorities, cobalt forms
both a chloride and hydrochlorate, indicated by a different color in the com-
pounds ; the chloride or binary compound obtained by concentration at a
high temperature being blue, while the hydrochlorate, like the non-binary
compounds nitrate and sulphate, although deprived of water, remain red.

Neutralization, in reference to salts, must be distinguished from saturation :
the first implies the destruction of the properties of acid and alkali by com-
bination, as manifested on organic colors ; the second the exhaustion of
chemical affinity. Potash is neutralized by combination with one atom of
sulphuric acid. The compound, sulphate of potash, presents neither acid
nor alkaline reaction ; it is a perfectly neutral salt. Potash will however
combine with an additional equivalent of acid forming a bisulphate ; in this
compound it is saturated with the acid, but the alkali is more than neutralized ;
it possesses a well-marked acid reaction. Potash in the state of bicarbonate
is saturated with carbonic acid ; it will take no more : but it is not neutral-
ized, for it presents a well-marked alkaline reaction. These terms are often
used as synonymous, but they have a widely different signification. The term
neutral salt is however commonly employed to signify the condition of a
compound without reference to the action of its solution on vegetable colors.
Provided the same equivalent weight of acid is present, the salt is neutral
although the solution may have an acid reaction. The sulphates of copper,
iron, and zinc contain the same proportion of acid to base as the sulphate of
potash, but while the latter is quite neutral, the three former are acid, and
redden litmus. The best test for neutrality is the blue infusion of cabbage,
prepared in the manner elsewhere described (page 76). It is reddened by
an acid, and changed to a green color by an alkali. To avoid confusion from
the use of the term neutral, Gmelin has proposed to call such salts normal.

In the double decomposition of salts it is usual to state that neutral salts
produce neutral compounds. This may be proved by adding to solutions of
sulphate of potash and chloride of barium respectively a small quantity of
blue infusion of cabbage. When mixed, there is a complete interchange of
acids and bases, but the mixed liquids remain blue. Hence there must have
been a complete substitution or replacement of acids and bases in equivalent
proportions ; in other words, the chloride of potassium and sulphate of baryta
are just as neutral as the compounds which form them. If an equivalent of
bisulphate of potash is employed, the blue liquid will be reddened by this
salt, and remain red after mixture, an equivalent of hydrochloric acid being
set free. When solutions of phosphates of soda and chloride of calcium,
colored with blue litmus, are mixed, the compounds, although neutral, so
decompose each other as to set free an acid, and the litmus is reddened.
This is owing to the formation of a basic phosphate of lime, i. e., a salt in
which the base predominates. An acid and an alkaline salt may by double
decomposition produce neutral compounds. A solution of alum reddened
by infusion of litmus or blue cabbage, when mixed with a due proportion of
a solution of carbonate of potash rendered green by infusion of cabbage,
will give rise to products of a neutral kind (sulphate of potash and hydrate
of alumina), and both liquids will become blue.



Online LibraryWilliam Thomas BrandeChemistry → online text (page 10 of 124)