13-1/4 lbs. alizarin paste (15 per cent.);
9 quarts thickening;
2 lbs. nitrate of alumina, at 29° Tw.;
15 oz. acetate of alumina, at 19° Tw.;
15 oz. red prussiate potash, dissolved in
water;
1 lb. 1 oz. acetate of lime, at 29° Tw.
To obtain a yellower shade, for every quart of mixed colour, 1 oz. bark
liquor, at 30° Tw., may be added.
Old spoiled red colours may be advantageously used for browns by adding
per quart, 3/4 oz. to 1 oz. red prussiate, dissolved in water.
=ALKALI.= _Syn._ ALKALI, Fr.; LANGENSALZ, Ger. This word has been used in
various senses, but is now usually applied to four substances only, viz.
the hydrates of potassium, sodium, lithium, and ammonium (the latter being
supposed to exist in the aqueous solution of ammonia). In a more general
sense it is applied to the hydrates of barium, strontium, and calcium,
which, for the sake of distinction, are called the alkaline earths. The
following properties are characteristic of the alkalies:--(1) They are
soluble in water, the alkalies proper more so than the alkaline earths.
(2) They change the hue of many vegetable colouring matters; thus, they
turn reddened litmus blue, yellow turmeric brown, and syrup of violets and
infusion of red cabbage green. (3) They neutralise the strongest acids.
(4) They precipitate most of the heavy metals from solutions of their
salts as hydrates or oxides. (5) They saponify the fixed oils and fats.
(6) They exert a caustic or corrosive action on animal and vegetable
substances.
=ALKALI ACTS.= The principal alkali Act is the 26 and 27 Vict., c. 24,
amended by 37 and 38 Vict., c. 43, the amended Act having come into
operation in 1875.
Every alkali work must be carried on so as to ensure the condensation of
not less than 95% of muriatic acid evolved therein; and it must be so
condensed that in each cubic foot of air, smoke, or chimney gases,
escaping from the works into the atmosphere, there is not contained more
than one fifth part of a grain of muriatic acid. Penalty for first
conviction, £50; for second and other offences, £100, or less (26 and 27
Vict., c. 124, s. 4; 37 and 38 Vict., c. 43, s. 4).
The owner of every alkali work is also bound "to use the best practicable
means of preventing the discharge into the atmosphere of all other noxious
gases arising from such work; or of rendering such gases harmless when
discharged."
The noxious gases are defined to be sulphuric acid, sulphurous acid
(except that arising from the combustion of coals), nitric acid, or other
noxious oxides of nitrogen, sulphuretted hydrogen and chlorine (37 and 38
Vict., c. 43, ss. 5 and 8).
The owner is liable for any offence against the Alkali Acts, unless he
prove that the offence was committed by some agent, servant, or workman,
and without his knowledge, in which case the agent, &c., is liable (26 and
27 Vict., c. 124, s. 5).
Every alkali work must be registered; penalty for neglect £5 per day
(ibid., s. 6).
Powers are given to owners to make special rules for the guidance of their
workmen (ibid. s. 13).
=ALKALIM'ETRY.= _Syn._ ALKALIME'TRIA, L.; ALCALIMÉTRIE, Fr. In
_chemistry_, the estimation of the strength of the commercial alkalies;
the art or process of determining the quantity or proportion of pure
caustic alkali, or of its carbonate, in any given sample or simple
solution. It is the reverse of 'acidimetry,' and it should be understood
that it does not apply to alkalies occurring under any other form or
condition than those just mentioned. Alkalimetric assays are now also
frequently and conveniently extended to the estimation of the alkaline
earths and their carbonates, as hereafter noticed.
_Alkalimetrical processes._ These, like those of 'acidimetry,' are for
the most part founded on--the capacity of the bases to saturate acids--the
estimation of the quantity of dry carbonic acid liberated from a given
weight of an alkaline carbonate under the influence of a stronger acid;
and, in the case of the pure alkalies, the sp. gr. of their solutions.
From any one of these results the exact amount of alkali, or of alkaline
carbonate, present in a sample, is easily found or calculated. These
processes are, indeed, precisely similar to those described under
ACIDIMETRY; but here the unknown quantity sought is the alkali, instead of
the acid.
_Assay._ The SAMPLE is drawn from as near the centre of the cask
containing the alkali as possible, and at once placed in a wide-mouthed
bottle, which is then closely corked up and numbered. Before proceeding to
the assay, the contents of the bottle are thrown on a piece of dry paper,
the lumps crushed small, and the whole reduced to coarse powder as rapidly
as possible. The number of grains required for the trial are then at once
weighed, placed in a phial or small glass tube, and agitated with about
1/2 oz. of hot water. After a short time allowed for repose, the clear
liquid is poured off into a beaker-glass or other vessel in which the
trial is to be made. This process is repeated with a second and a third
quantity of water, or until nothing soluble remains, shown by the last
washings not affecting the colour of turmeric paper. The greatest care
must here be taken not to waste the smallest portion of the liquid, which
would render the results inaccurate.
To the solution in the beaker-glass a little solution of litmus is added,
unless the acid is tinted with it when it is unnecessary. The solution is
now heated until near its boiling point, and a piece of white paper or
porcelain put behind it, to better show up the changes of colour. The
alkaline solution is now treated with the standard test-acid, which is
poured carefully from an alkalimeter or Mohr's burette, until the
solution, after turning a purple red, suddenly assumes a pink colour.
Neutralisation being thus effected, the operator allows the sides of the
alkalimeter or burette to drain, and then either 'reads off' the number of
divisions which have been consumed, or (if using the test-acid by weight)
determines the quantity by again weighing the alkalimeter. The common
practice is to allow two drops (= 1/5th of an alkalimetrical division by
VOLUME, or 2 gr. by WEIGHT) for over-saturation, which is, therefore,
deducted from the 'observed quantity' of the test-liquor employed.
In testing solutions of the PURE or CAUSTIC ALKALIES, the colour, on
neutralisation, suddenly changes from blue to pink or red, without any
intermediate vinous or purple colour being produced.
The quantity of test-acid used gives the absolute or per-centage
composition of the sample examined, according to the constitution of the
test-acid used.
_Standard Acids._ The various test-acids in use as described below, each
being used by different operators as they think best.
The most convenient test-acid, or normal solution, both for commercial and
chemical assays, is perhaps dilute sulphuric acid, which, when intended to
be used VOLUMETRICALLY, has the sp. gr. 1·032 at 60° Fahr., and contains
in 100 alkalimetrical divisions 1000 water-grains measure, or 1 litre,
exactly 49 gr. (or grammes) of sulphuric acid; and when intended to be
used GRAVIMETRICALLY, or by weight, has the sp. gr. 1·033, and contains in
1000 gr. (or grammes) weight exactly 49 gr. (grammes) of sulphuric acid;
and, in both cases, consequently corresponds to 1 equiv. of every other
base. These dilute acids are easily prepared by mixing 1 part of the
concentrated acid with 11 or 12 parts of distilled water; the precise
quantity depending on the strength of the acid employed, and must be so
arranged that 1000 grains shall exactly neutralise 1000 grains of water
containing 53 grains of pure anhydrous sodium carbonate.
This acid (as well as all those hereafter mentioned) may be kept faintly
tinged with litmus, which is often more convenient than tinging the
alkaline solution at the time of making the assay.
It will at once be seen that every alkalimeter division of the first of
the above acids, and every 10 gr. of the second, represent the 1/100th
part, or 1% of alkali whenever the equivalent weight[18] of the latter is
taken for the assay. Every 1-10th part of an alkalimeter-division (or
every drop), and every grain weight (when a Schüster's alkalimeter is
employed) then respectively represents the 1/10 of 1%; and the result
sought is obtained without the necessity of any calculation.
[Footnote 18: See Table II, at the end of this article.]
This is obvious--for if the equivalent of a pure alkali or of
its carbonate (_i. e._ one of 100%) requires an equiv. (100
alkalimeter-divisions, or 1000 gr.) of test-acid to saturate it, an alkali
or alkaline carbonate of 75%, 50%, or 25%, will respectively require only
75, 50, or 25 divisions, or 750, 500, or 250 gr.; and so of other
strengths in proportion. The only precaution necessary is always to take
the standard weight for the assay answering to the equiv. of the
denomination of the per-centage result sought. Thus, in testing a
carbonate of potash, we may either wish to determine its per-centage
richness in 'dry carbonate,' or in 'pure potassa,' the latter being
usually the case. To obtain the first, we must take 69 gr. for the assay;
and to obtain the second, 47 gr. With _CAUSTIC ALKALIES_, or mixtures
containing them, the weight, in grains, taken for the assay, must always
correspond to the equiv. of the pure base. See Table II, at the end of
this article.
In _commercial assays_, when 100 gr. (or some aliquot part thereof) are
taken for trial, the per-centage result is obtained from the number of
alkalimeter-divisions, or the number of grains, of the test-acid consumed,
by the common Rule of Proportion. Thus:--A crude sample of potash having
taken 90 alkalimeter-divisions of test-acid to neutralise it, would
contain--
100 : 47 :: 90 : 42·30%
or nearly 42-1/3 per cent. of pure potassa. If only 50, 25, or 20 gr. are
tested, the result must, of course, be double, quadruple, &c., as the case
may be. Or the third term of the proportion may be multiplied by the
denominator of the fraction representing the aliquot part. This, in the
case of 50 gr. (repeating the above example), would be--
10 : 47 :: 45 × 2 : 42·30%
as before; but even these easy calculations may be simplified, as is shown
below.
One of the advantages, and not the least, attending the use of test-acids
corresponding to equivalents, is, that by means of the simple Rule of
Three, the per-centage quantity of alkali may be found whether 100 or any
other number of grains have been submitted to trial. For--The weight of
the sample tested (in grains) bears the same relation to the equivalent
weight of the alkali under examination, that the number of
alkalimeter-divisions or of the grains of test-acid consumed do to the
per-centage of alkali sought. Thus, with a sample of 33 gr. of pearlash
taking 35 alkalimeter-divisions or 350 grains (every 10 gr. being = 1%) of
test-acid for neutralisation, this would be--
33 : 47 :: 35 : 49·85%
or nearly 50 per cent. of pure potassa. By substituting the equiv. of the
dry carbonate of potash (69), for that of pure potassa used above, the
quantity of that article corresponding to the same weight of the pure
alkali may be at once found. Repeating the last example this will be--
33 : 69 :: 35 : 73·18%
or nearly 73-1/4 per cent. The same applies to all the alkaline bases and
their carbonates.
For commercial purposes, there is used, amongst others, an empirical
solution, as a test-acid for potassa, soda, and ammonia, to save the
necessity of calculation.
This is dilute sulphuric acid having a sp. gr. of about 1·071; 100
alkalimeter-divisions (1000 water-grains measure) exactly saturate 100 gr.
of pure potassa, or 113 gr. of anhydrous carbonate of soda. The number of
measures consumed, read off by mere inspection from the scale of the
alkalimeter, gives the exact per-centage of alkali in the sample examined,
for POTASH; and by multiplying it by ·66, that for SODA also. By employing
·362 as the multiplier, it gives the like result for AMMONIA. In fact,
occasionally, in order to save the necessity of any calculation, two
'test-acids' are frequently employed--the one for potash and the other for
soda.
These are made by diluting sulphuric acid to a sp. gr. of near 1·071 and
1·086 respectively; 1000 grains, by measure, of the first neutralising
exactly 100 grains of pure potassa, or 113 of pure anhydrous soda
carbonate, and the latter neutralising exactly 100 grains of pure soda, or
171 gr. of pure anhydrous sodium carbonate.
There is another system of preparing standard acids by means of a
Faraday's alkalimeter. A strong acid is prepared by diluting sulphuric
acid to a sp. gr. of 1·1268 at 60°, and 455·7 grains exactly neutralise
100 of anhydrous carbonate of soda.
The glass tube here referred to, and known as Faraday's ALKALIMETER, is
graduated centesimally, in the usual manner; but opposite the numbers
22·1, 48·62, 54·43, and 65, are cut the words 'soda,' 'potassa,'
'carbonate of soda,' and 'carbonate of potassa,' to indicate the quantity
of the test-acid to be employed for each of these substances. (See
_engr._) It is used by pouring the test-liquor into it until it reaches
the line marked against the alkali, or carbonate, under examination, the
remaining divisions being filled up with pure water, and the whole well
mixed by placing the thumb on the orifice of the tube and shaking it well.
The measure of the resulting dilute acid must then be very carefully
observed, and more water added, if required, to bring it up to the zero
(0) or 1000 gr. on the scale; careful agitation being again employed as
before. The test-acid thus prepared is then added, with the usual
precautions, to the sample until exact neutralisation is effected. The
quantity consumed for this purpose, read off from the graduated scale,
expresses the exact per-centage of the pure ALKALI, or of its CARBONATE,
as the case may be, contained in the sample examined, provided 100 gr.
have been taken for the assay.
[Illustration]
Another method sometimes used is that of M. Mohr, and practised as
follows:--The alkaline solution, slightly coloured blue with litmus, is
strongly super-saturated with a standard acid (sulphuric or oxalic) of
known strength, supplied from an alkalimeter in the usual manner; the last
traces of carbonic anhydride being removed by boiling, shaking, blowing
into the flask, and, finally, sucking out the air. A standard solution of
caustic soda (of a strength exactly corresponding to that of the test-acid
already used) is now cautiously added, drop by drop, until the colour,
rendered yellowish-red by the acid, just appears of a light blue. The
difference between the quantity of the solution of the test-alkali and of
the test-acid consumed, expresses the exact quantity of acid neutralised
by the alkali, and hence also its strength.
Besides the above methods, the alkaline carbonates are analysed, by the
loss of carbonic anhydride (carbonic acid) they suffer, by being
decomposed by a strong acid. The best method in use is that of MM.
Fresenius and Will, and depends on the same principle, and is performed in
a similar manner and in a similar apparatus to that described under
ACIDIMETRY; the only difference being that here the uses of the small tube
(_e_) is dispensed with, and that the alkali is tested under the form of
carbonate, instead of bicarbonate.
_Oper._ The smaller flask (_B_) is about half filled with concentrated
sulphuric acid, and the sample of alkali, in solution (under the form of
carbonate), being placed in the larger flask (_A_), water is added until
it is about one third full. The tubes are then fitted into the apparatus
quite air-tight; the end of the tube (_b_) is fastened with a piece of
wax, and the whole is very carefully weighed. The apparatus is now removed
from the scales, and a perforated cork, or a small piece of india-rubber
tube, being temporarily applied to the end of the tube (_h_), a few
bubbles of air are sucked out of the flask (_B_) by means of the lips; the
consequence of which is, that on removing the mouth the acid in (_B_)
ascends to a certain height in the tube (_c_). If in a short time this
little column of liquid maintains its height in the tube, it is a proof
that the apparatus is perfectly air-tight, and as it should be. Suction is
now again cautiously applied to the tube (_h_) and a little of the acid in
(_B_) made to flow over into the flask (_A_), the quantity being
proportionate to the vacuum produced by suction, and capable of being
regulated at will. No sooner does the acid come into contact with the
carbonate in the flask (_A_) than the evolution of carbonic acid
commences, and this, from the construction of the apparatus, having to
pass through the concentrated sulphuric acid, is rendered quite dry before
it can escape by the tube (_d_) into the atmosphere. Whenever the
effervescence flags, a little more acid is sucked over, until the whole of
the carbonate is decomposed; after which an additional quantity is made to
pass into (_A_), so as to raise the temperature considerably, for the
purpose of expelling all the gas absorbed by the fluid during the
operation. As soon as this is effected, the wax is removed from the
aperture (_b_), and suction applied to (_h_), until all the carbonic acid
in the apparatus is replaced by atmospheric air. The whole is now allowed
to cool, and (together with the piece of wax removed) is again accurately
weighed. The loss of weight gives the exact amount of dry carbonic
anhydride, or anhydrous carbonic acid, which was contained in the
specimen, from which the weight of PURE ALKALI is readily estimated, as
every 22 gr. of dry carbonic acid gas evolved represents exactly 31 gr. of
pure SODA, 47 gr. of pure POTASSA, &c. &c.; these numbers being the
equivalents of the respective substances from which the per-centage
strength may be found by the rule of proportion, as before explained.
Thus, in the case of a 100-gr. sample of carbonate of soda which has lost
15-1/4 gr. of carbonic acid, by the assay, this would be--
22 : 31 :: 15-1/4 : 21·48%
or nearly 21-1/2 per cent. of pure soda. If 53, the equiv. of anhydrous
carbonate of soda, be taken, instead of 31 (the eq. of pure soda), the
answer would have been, in the terms of that substance, 36·748%, or nearly
36-3/4 per cent. When an aliquot part of 100 gr. has been taken for the
assay, either the result, or the third term of the proportion, must, of
course, he multiplied by the denominator and divided by the numerator of
the fraction representing such aliquot part.
By multiplying the weight of carbonic anhydride lost, by the numbers
opposite the names of the respective alkalies and their carbonates in the
second column of the following _Table_ the equivalent per-centage value of
the carbonates examined may be obtained in terms corresponding to the
various denominations named therein, when 100 gr., or any aliquot part of
100 gr., have been tested; the result, in the latter case, being, of
course, multiplied as before.
By taking certain standard weights for the assay, the quantity of carbonic
acid evolved may be made to furnish the per-centage strength or value of
the specimen in the terms of either the pure or carbonated alkalies,
whether in their anhydrous or hydrated state. The numbers in the second
column of the following _Table_ represent the quantity in grains and
decimal parts of each of the substances named in the first column,
equivalent to one grain of carbonic anhydride. These numbers, as already
mentioned, may be employed as factors for converting any numbers
representing grains of that acid into the equivalents of these substances,
true to 4 places of decimals; and further, they furnish us with the data
for determining the exact number of grains which must be tested, so that
the loss of weight in carbonic anhydride shall at once give us the
per-centage richness of the sample in the terms of the denomination for
which it is taken. The numbers in the third column of the _Table_, formed
by simply moving the decimal point of the numbers in the second column one
figure further to the right, indicate the weights to be taken for the
assay, so that the loss of weight, reckoned in tenths of a grain, exactly
represents the per-centage strength in the terms sought. The weights
corresponding to the numbers in the fifth column give the same results,
provided the loss of weight is reckoned in quarter-grains; those in the
sixth column effect the same when the loss of weight is reckoned in
half-grains; whilst those in the last column require that the gas
eliminated should be counted in grains, and are simply the numbers in the
second column of the _Table_ multiplied by 100, or reproduced by moving
the decimal point two figures to the right.
TABLE I.--_Multipliers and Standard Weights for the
Principal Alkalies and their Carbonates._ (COOLEY.)