Cooley's Cyclopaedia of Practical Receipts Volume I Part 6

_Obs._ The above are the processes usually adopted, on the large scale, in this country.

3. (M. Mollerat's process--without distillation.) Pure commercial acetate of soda, in coa.r.s.e powder, is placed in a hard glazed stoneware or gla.s.s pan or receiver set in a cool situation, and 35% or 36% of concentrated sulphuric acid, of the sp. gr. 1843, added, in such a manner that the acid may flow under the powder, and little heat be generated by the operation; the whole is then allowed to remain in contact (covered) for some hours, when crystalline grains of sulphate of soda are found covering the bottom and sides of the vessel, and hydrated acetic acid, partly liquid and partly in crystals, the upper portion. The temperature being now slightly raised to a point just sufficient to cause the liquefaction of the crystals of acetic acid (_i.e._, to from 62 to 65 Fahr.), the fluid is poured off, and a very small quant.i.ty of pure acetate of lime added to it gradually, until it ceases to yield any trace of free sulphuric acid on evaporation. After sufficient repose it is carefully decanted for use. An excellent commercial strong acetic acid is thus obtained, without distillation, owing to the insolubility of sulphate of soda in acetic acid; and from which glacial acid may be procured by refrigeration. If, however, the process be badly managed, or the proportions of the ingredients be not carefully observed, the product will be contaminated with either a little sulphuric acid or saline matter. It is also important to the success of this process that it be performed in a cool apartment, and in well-cooled vessels. Perfectly pure acetic acid may easily be obtained by rectification from this acid. The above plan of superseding a troublesome distillation is one of the greatest improvements yet introduced into the manufacture of acetic acid.

4. (Liebig's process.) Pure acetate of soda, thoroughly dried and finely powdered, 3 parts, is placed in a capacious retort, and pure concentrated sulphuric acid, 97 parts, poured over it through the tubulature. One eighth of the acetic acid pa.s.ses over by the heat developed by the reaction of the ingredients. The heat of a sand bath is next applied and continued until the contents of the retort become quite liquid. The distillate, carefully rectified, yields two parts of pure acid, containing only 20 per cent. of water. On exposing the latter portion which comes over in a closed vessel to a temperature below 40 Fahr., crystals of hydrated acetic acid are deposited. The weaker, or liquid portion, being poured off, the crystals are again melted and re-crystallised by cooling.

The crystals of the last operation, separated from the liquid, and carefully drained in a cool and closed vessel, are perfectly pure hydrated acetic acid.

_Obs._ The above is an excellent process for obtaining a chemically pure acid. The excess of sulphuric acid left from the process may be recovered by distillation; or the whole residuum may be employed in a second distillation with fresh acetate.

[Ill.u.s.tration: (_C._) A Liebig's Condenser. (The other _reference letters_ are self-explanatory.)]

Although a retort is recommended by Liebig for the distillation, and is usually adopted, on the small scale, for the purpose, a flask closed by a cork perforated by two tubes, as exhibited by the _engr._, will be found more convenient and safe; as the product is then less likely to be contaminated by the 'spirting' of the ingredients over the brim of the vessel. The heat of a diffused gas-flame may also be often advantageously subst.i.tuted for a sand bath.

_b._ From ACETATE OF POTASH:--

1. Acetate of potash (fused and powdered) is placed in a still, or other suitable vessel, and 50% of the strongest sulphuric acid ('oil of vitriol'

of fully 184 sp. gr.) being added, the mixture is distilled to dryness, as before. The product is 50 to 51% of the weight of the acetate employed, with a sp. gr. of about 10735 to 1074, containing about 66% of anhydrous acetic acid, or nearly 80% of ordinary glacial acid. By rectification from a little dried acetate of lead a perfectly pure acid of almost any strength may be obtained. The ingredients are nearly in equiv.

proportions.

_c._ From ACETATE OF LEAD:--

1. (Ure.) Take of dried acetate of lead, 4 parts; strongest oil of vitriol, 1 part. Distil slowly to dryness. Nearly equal to the last.

2. (Liebig.) Acetate of lead, 3 parts; sulphuric acid, 8 parts; as before.

3. (Dollfuss' Concentrated Acetic Acid.) Take of dried acetate of lead, 12 oz.; sulphuric acid, 6 oz.; distil 7 ounces.

_d._ From ACETATE OF LIME:--

1. (Christl.) Raw acetate or pyrolignate of lime (prepared by Volckel's process), 100 parts, is mixed with hydrochloric acid (20 Baume, or sp.

gr. 11515), 120 parts; and after 12 hours, distilled in a copper vessel, with a gradually applied heat. The product is 100 parts or lbs. of acetic acid of 8 Baume (sp. gr. 10556), containing about 47% of hydrated acid, only slightly coloured and empyreumatic, fit for various manufacturing purposes. The advantage of this process is the low price of hydrochloric acid, and the product not being contaminated with sulphuric or sulphurous acid.

_Obs._ It will be found that pyrolignate of lime generally contains 60% to 70% of neutral acetate; but should it contain either more or less, a proportionate quant.i.ty must be employed. When the proper proportions are used the distillate gives only a scarcely perceptible turbid cloud when tested with nitrate of silver. If the hydrochloric acid used has the sp.

gr. 116, a less quant.i.ty being employed, the product will have the sp.

gr. of 1058 to 1061, and will then contain from 48 to 51% of the monohydrate, or 41 or 42% of anhydrous acetic acid. The resin sometimes found floating on the mixed ingredients should be carefully removed, by skimming, before distillation.

As acid of the above strength is rarely required, and as the distillation is more easily conducted when the ingredients are less concentrated, a little water may be conveniently added either before or towards the end of the distillation. Hence the following proportions have been recommended:--

2. (Volckel.) Acetate of lime (as last), 100 parts; hydrochloric acid (sp.

gr. 116), 90 to 95 parts; water, 25 parts; mix, and proceed as before.

Prod. 96 to 98 parts of an excellent acid, well adapted to trading purposes, having a sp. gr. about 1050, and containing nearly 40% of hydrated acetic acid. It has been correctly remarked, that the acetic acid produced with hydrochloric acid is always of better quality than that produced with sulphuric acid; being not only less coloured, but also entirely free from sulphurous acid. The distillation uniformly proceeds with ease and regularity, and the whole of the acetic acid pa.s.ses over between 212 and 248 Fahr.; by which the danger of contamination with other products, resulting from a high degree of heat, is obviated.

3. An Acetic acid sufficiently strong and pure for many ordinary purposes may be obtained without distillation, by pouring strong sulphuric acid, 60 parts, diluted with water, 5 parts, on well-dried acetate of lime, 100 parts; digesting, with occasional agitation in a close vessel, decanting the clear liquid, and straining the remainder.

[Ill.u.s.tration:

_A_, Furnace.

_B B B B_, Gla.s.s receivers.

_C_, Stoneware retort.

_D_, Bottle containing vinegar.

_E E E E_, Basins containing water.

_F F F F_, Supports for basins.

_G_, Welter safety-tube.

_H_, Supply-pipe of cold water.

_I I I I_, c.o.c.ks to supply water to the basins.

_J_, Water main.

_L_, Adapter connecting retort and globes.]

II. _From_ the _Acetates_ by _dry distillation_ with a _sulphate_:--

_a._ From ACETATE OF LEAD:--

1. Acetate of lead (dried), 5 parts; and sulphate of iron (gently calcined), 2 parts; are separately powdered; and after thorough mixture, carefully distilled, by the heat of a sand bath, into a well-cooled receiver. An economical process for a strong acid, under certain circ.u.mstances; but one now seldom adopted.

2. (Bardollier's Strong Acetous acid.) Dried acetate of lead, 10 oz.; calcined green vitriol, 12 oz.; as the last.

_b._ From the ACETATES OF COPPER:--By subst.i.tuting acetate or diacetate of copper, in equiv. proportions, or better with excess of the sulphate.

Seldom used.

_c._ From ACETATE OF POTASH, as the last.

III. From the _Acetates per se_:--

_a._ From ACETATE OF COPPER:--AROMATIC V.; SPIRIT OF VERDIGRIS; SPIRITUS VEN'ERIS, L.; ESPRIT DE VENUS, Fr.; ACIDUM ACE'TIc.u.m, (Ph. L. 1787.) _Process._ Carefully dry crystallised verdigris (diacetate of copper) by a very gentle heat, and introduce it into a large stoneware retort (see _engr._), the bottom of which has been previously coated with a mixture of clay and horse-dung, to render it more capable of standing the fire. Next place it in a suitable furnace, and connect it, by an adapter, with 3 or 4 double tubulated globes, the last of which must be furnished with a vertical tubulature, to which a double Welter's safety-tube should be adapted; the other end being immersed in a basin half-filled with distilled vinegar or water, while the funnel portion communicates with the atmosphere. Then place each globe in a basin of water, kept cool by a stream constantly pa.s.sing through it; and cover the upper portion with cloths kept continually wet with cold water. After 15 or 20 hours, fire may be applied, and must be so regulated that the drops follow each other with considerable rapidity from the end of the adapter, whilst the bubbles of air cause no inconvenience at the other end of the apparatus. If otherwise, the fire must be damped a little. The operation should be continued, and the fire gradually increased, until vapour ceases to come over, known by the globes gradually cooling, notwithstanding the heat of the furnace. The operation being concluded, the whole may be allowed to cool, and the acid collected preparatory to rectification. This may be effected in a similarly arranged apparatus, except that it must be wholly of gla.s.s; and the retort should not be much more than half-filled. The operation must now be very carefully conducted, and discontinued before barely the whole of the acid has distilled over; as the last portion is apt to injure the flavour and colour of the rest. The first portions which come over are very weak, and should be kept separate, until the sp. gr.

reaches to about 1372, when the receiver should be changed, and the product collected in separate portions, as noticed below.

_Obs._ Good diacetate of copper yields, by careful management, at a temperature of 400 to 560 Fahr., fully one half its weight of a greenish-coloured acid, of the sp. gr. of about 1061, containing above 50% of hydrated acetic acid, or 43% of anhydrous acid. 20 lbs. of the ordinary acetate yields 9-3/4 lbs. of this rough acid, leaving a residuum of about 6-1/2 lbs. of metallic copper mixed with a little charcoal, in the retort; the remainder (nearly 2/10ths of the acid in the acetate) being decomposed by the heat, and lost. This 9-3/4 lbs. of crude acid yields by rectification, and dividing the products, 1/2 lb. of acid of the sp. gr. 1023; 3 lbs. of the sp. gr. 1042; and 6 lbs. of the sp. gr.

1065; exclusive of a little acetone which comes over with it. In the first distillation, the strongest acid is found in the third receiver, and the weakest in the first. The acid obtained in this way is always accompanied with a little fragrant pyro-acetic spirit; which renders it preferable for aromatic vinegar and perfumery. It dissolves camphor, resins, and essential oils with facility. This is one of the oldest methods of obtaining glacial acetic acid, and the product is still preferred for some purposes. It is the RADICAL VINEGAR of the alchemists, and it is that which is preferred by the perfumers. Well-dried acetate of lead, or of iron, as well as several other acetates, may be subst.i.tuted for acetate of copper in the above process; but are less economical and convenient. In all cases, great care must be taken to avoid over-firing, as thereby the quant.i.ty obtained is lessened, and the quality injured. The residuum of the distillation is pyrophoric and frequently inflames spontaneously, on exposure to the air. Due caution must be therefore observed regarding it.

IV. _From Wood_, by _dry distillation_. See PYROLIGNEOUS ACID. The preparation of the purified acid, by converting it into an acetate, and subsequent distillation with a strong acid, is noticed _above._

[Ill.u.s.tration]

V. _From Alcohol._ (ALCOHOL VINEGAR, GERMAN ACETIC ACID.) In a bell-gla.s.s, or an oblong gla.s.s case, perforated shelves are arranged, a few inches apart, one above another, on which are placed a number of small flat dishes of porcelain, earthenware, or wood. These dishes are filled with spirit of wine or dilute alcohol; and over each is suspended a watch-gla.s.s or capsule containing a portion of platinum-black; the whole being arranged so that the platinum-black and the surface of the alcohol are not more than 1-1/2 to 2 inches apart. Strips of porous paper are next so hung in the case, that their bottom edges are immersed in the spirit, to promote evaporation; and lastly, the apparatus, loosely covered, is set in a light place at a temperature of from 70 to 90 Fahr.--the sunshine, when convenient. In a short time the temperature of the platinum rises, and the formation of acetic acid begins; and the condensed vapour trickles down the sides of the gla.s.s and collects at the bottom of the case, whence it is removed once or twice a day. (See _engr._) The product of a case of twelve cubic feet content, with 7 or 8 oz. of platinum-powder, is capable of producing daily, if well managed, nearly 131 lb. of hydrated acetic acid from 1 lb. of absolute alcohol; 25 lbs. of platinum-powder and 300 lbs. of alcohol will, in like manner, furnish a daily supply of nearly 350 lbs. of pure acid, and of other strengths in proportion. Theoretically, the product should be 130 parts of the hydrated acid for every 100 parts of alcohol consumed; but this is never quite obtained in practice, owing to a small portion of the alcohol mixing with the newly formed acid, and escaping decomposition; and from another small portion of both the alcohol, and of the newly formed aldehyd, being carried off by the air that permeates the apparatus. The platinum-powder does not waste, and the most inferior spirit may generally be employed.

_Rationale._ In this process, the alcohol (as in other cases of acetification) is first converted into aldehyd; and this, as rapidly as formed, absorbs oxygen and pa.s.ses into hydrated acetic acid. The simultaneous formation of aldehyd during the oxygenation of that already formed, may be detected by its odour.

_Obs._ During the mutual action of the platinum-black and the vapour of alcohol, the temperature increases, and continues to do so until all the oxygen contained in the air enclosed in the case is consumed, when the acetification stops. On opening the case for a short time, to admit of a fresh supply of air, the operation recommences, thus showing its dependence on the oxygen of the atmosphere. For this trans.m.u.tation, 100 grains of alcohol require 71 grains (equal to 200 cubic inches) of oxygen, or about 1000 cubic inches of atmospheric air. To render the process continuous and rapid, a fresh supply of air must, therefore, be constantly provided. This may be effected by either having a loosely covered opening at the top of the case, and several much smaller ones near its lower part; or (and preferably) by means of two small gla.s.s tubes pa.s.sing through the lid or cover, one of which terminates just below the point of insertion, whilst the other divides into branches which reach to within a short distance from the bottom, as shown in the _engraving_. In this way a very slow current of fresh air will always be kept up in the apparatus.

[Ill.u.s.tration]

In practice, we find, that by loosely spreading the platinum-black on pieces of platinum-gauze, and supporting these on small tripods or bars of gla.s.s or porcelain (or even wood), the watch-gla.s.ses and their troublesome suspension may be dispensed with; as also may be the strip of porous paper, provided a temperature of not less than 90 Fahr. be maintained in the case or acetifier, which may easily be done by the application of artificial heat in the absence of sunshine. On the large scale, a case of wood with a gla.s.s roof, or even a well-seasoned cask or vat may be employed, in which case the temperature of the apparatus must be kept up either by means of steam-pipes or flues, or by the supply of warm air. On the small scale, a hand bell-gla.s.s placed on a dish, with a single watch-gla.s.s or piece of platinum-gauze, and a single capsule containing alcohol, may be used, provided the bell-gla.s.s be supported on three very small wedges, to admit of a supply of air. A modification of this is sometimes employed, in which the alcohol is supplied, in drops, to the platinum-black, by means of a long, tubular funnel pa.s.sing through the mouth of the bell-gla.s.s, and having its lower extremity drawn to a very fine point, as shown in the _engr._ To ensure success, the platinum-black should be either fresh-prepared, or recently washed and very gently heated, before placing it in the acetifier. Spongy platinum, though ordered by many chemical compilers, does not answer well for this process.

By the above elegant and economical process, perfectly pure acetic acid of considerable strength may be produced from even impure alcohol; but it is impossible in this way to obtain a concentrated acid without a subsequent operation, because the action of platinum-black on absolute alcohol, or even on strong alcohol, is so violent that the platinum soon begins to glow, and inflammation ensues. Unfortunately the revenue laws of this country, until lately, stood in the way of the adoption of this beautiful process, unless duty-paid alcohol or methylated spirit be employed; but there is no statute that prevents an individual employing pure spirit, of any strength, on the small scale, for private consumption. In Germany, and in the United States of America, vinegar is manufactured on this plan, and from the low price of crude alcohol there, it will no doubt prove ultimately to be the cheapest source of both pure acetic acid and culinary vinegars.

VI. _Miscellaneous Formulae_:--

1. An excellent acetic acid, of considerable strength, may be made by soaking fresh-burnt and perfectly dry charcoal in common vinegar, and then subjecting it to distillation. The water comes over first, and on increasing the heat, the acid follows. Vinegar-bottoms and waste vinegar may be used.

2. By exposing vinegar, or dilute acetic acid, to the air in very cold weather, or to freezing mixtures, the water separates in the form of ice, and the strong acetic acid may be obtained by draining it into suitable gla.s.s vessels, observing to do so at a temperature sufficiently low to keep the water solid. Said to answer well in cold climates.