Cooley's Cyclopaedia of Practical Receipts Volume I Part 27

=ALKALI ACTS.= The princ.i.p.al 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.; ALCALIMeTRIE, Fr. In _chemistry_, the estimation of the strength of the commercial alkalies; the art or process of determining the quant.i.ty 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 a.s.says 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 quant.i.ty 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 quant.i.ty sought is the alkali, instead of the acid.

_a.s.say._ 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 a.s.say, the contents of the bottle are thrown on a piece of dry paper, the lumps crushed small, and the whole reduced to coa.r.s.e powder as rapidly as possible. The number of grains required for the trial are then at once weighed, placed in a phial or small gla.s.s 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-gla.s.s or other vessel in which the trial is to be made. This process is repeated with a second and a third quant.i.ty 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-gla.s.s 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 a.s.sumes 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 quant.i.ty 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 quant.i.ty' 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 quant.i.ty of test-acid used gives the absolute or per-centage composition of the sample examined, according to the const.i.tution 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 a.s.says, is perhaps dilute sulphuric acid, which, when intended to be used VOLUMETRICALLY, has the sp. gr. 1032 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. 1033, 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 quant.i.ty 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 a.s.say.

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 a.s.say. Every 1-10th part of an alkalimeter-division (or every drop), and every grain weight (when a Schuster'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 a.s.say 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 pota.s.sa,' the latter being usually the case. To obtain the first, we must take 69 gr. for the a.s.say; and to obtain the second, 47 gr. With _CAUSTIC ALKALIES_, or mixtures containing them, the weight, in grains, taken for the a.s.say, must always correspond to the equiv. of the pure base. See Table II, at the end of this article.

In _commercial a.s.says_, 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 : 4230%

or nearly 42-1/3 per cent. of pure pota.s.sa. 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 : 4230%

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 quant.i.ty 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 : 4985%

or nearly 50 per cent. of pure pota.s.sa. By subst.i.tuting the equiv. of the dry carbonate of potash (69), for that of pure pota.s.sa used above, the quant.i.ty 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 : 7318%

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 pota.s.sa, soda, and ammonia, to save the necessity of calculation.

This is dilute sulphuric acid having a sp. gr. of about 1071; 100 alkalimeter-divisions (1000 water-grains measure) exactly saturate 100 gr.

of pure pota.s.sa, 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 1071 and 1086 respectively; 1000 grains, by measure, of the first neutralising exactly 100 grains of pure pota.s.sa, 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 11268 at 60, and 4557 grains exactly neutralise 100 of anhydrous carbonate of soda.

The gla.s.s tube here referred to, and known as Faraday's ALKALIMETER, is graduated centesimally, in the usual manner; but opposite the numbers 221, 4862, 5443, and 65, are cut the words 'soda,' 'pota.s.sa,'

'carbonate of soda,' and 'carbonate of pota.s.sa,' to indicate the quant.i.ty 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 quant.i.ty 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 a.s.say.

[Ill.u.s.tration]

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 quant.i.ty of the solution of the test-alkali and of the test-acid consumed, expresses the exact quant.i.ty of acid neutralised by the alkali, and hence also its strength.

Besides the above methods, the alkaline carbonates are a.n.a.lysed, 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 quant.i.ty 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 pa.s.s 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 quant.i.ty is made to pa.s.s 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 POTa.s.sA, &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 a.s.say, this would be--

22 : 31 :: 15-1/4 : 2148%

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, 36748%, or nearly 36-3/4 per cent. When an aliquot part of 100 gr. has been taken for the a.s.say, 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 a.s.say, the quant.i.ty 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 quant.i.ty 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 a.s.say, 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 Princ.i.p.al Alkalies and their Carbonates._ (COOLEY.)

KEY:

A - Factors or Multipliers for converting the weight of carbonic acid expelled into real strengths.

B - Quant.i.ty (in grains) to be taken, so that the per-centage value of the sample tested shall be shown in the terms of any of the denominations given, by the weight of the evolved Carbonic Acid reckoned-- C - in tenths of a grain.