When working upon commercial acetate of lime,the acetate is previously roasted so as to destroysome of its impurities. For this purpose a largeiron retort is employed, 3 feet 6 inches in diameter,and 6 feet long; near the bottom a grating is soarranged as to touch the sides of the retort at a fewpoints only, in order that conduction of heat fromthe sides may be but small. The acetate of lime isplaced in sheet-iron trays about 2 inches deep, whichare placed in the grating one over the other untilthe retort is filled; the trays are separated by ironrods laid in between them, and care is taken to keepthem out of contact with the sides of the retort.The retort is then gradually fired until the outletor head passing from the retort becomes heated bythe escape of steam, after which the fire is steadilykejrt up but not raised higher until this escape pipecommences again to cool down, which indicates thatthe greater part of the water and the impurities havebeen driven off. The fire is now let out, and whencool, or nearly so, the charge is drawn. The oper-ation generally takes about forty-eight hours for itscompletion.
When a solution of acetate of lime obtained byneutralizing impure acetic acid is operated upon,the aeeto-chloride may be similarly roasted beforeredissolving and recrystallizing it. Boasting theaceto-cliloride may also be done when working oncommercial acetate of lime in place of roasting theacetate. Or in lieu of roasting, the original solutionof acetate and chloride, or the acetate of lime alone,is sometimes filtered through animal charcoal, whichhas a remarkable affinity for, or power of, separatingthe empyreumatic impurities from the aceto-chloridc,and also, though in a much less degree, from acetateof lime.
To make acetic acid, the calcium aceto-chloride,purified by crystallization, is decomposed withhydrochloric, sulphuric, or any other acid having suffi-cient affinity for lime to liberate the acetic acid con-tained in the salt, and the acetic acid separated fromthe chloride, and sulphate, or other calcium salt, bydistillation.
The plan adopted is as follows :—To 112 parts ofcalcium aceto-chloride, 24 parts of sulphuric acid,spec. grav. l - 84f>, or thereabout, diluted with twiceits volume of water, are added; these materialshaving been well mixed, are then distilled, and theacetic acid condensed in the usual manner. Torender this acid quite pure, /.<?., free from hydro-chloric acid, it is again distilled off alkali or acetateof soda, employed in the proportion of 1 lb. to 10gallons of acid.
Another method is to take of aceto-chloride ofcalcium 100 parts, and of hydrochloric acid, spec,grav. 1T60, 50 parts each by weight, and after care-fully dissolving the former in the latter, distillingoff the acetic acid and condensing it as usual. Thisoperation is performed in a suitable still, and in themanner usually followed in the manufacture of aceticacid by the decomposition of acetate of lime withhydrochloric acid. This acid is also redistilled withsufficient alkali to retain any slight trace of hydro-
-Condy’s Process.
chloric acid which may have passed over with thevapour in the first operation. The aceto-chloride isfrequently sent into the market to be used by thepurchaser as a convenient source of acetic acid.This process has the groat advantage over manyothers that the preparation of the aceto-chloride canbe conducted on the spot whore wood is distilled, asfor example, in foreign countries where wood ischeap, and may then be imported into this countryfor the process of producing the pure acetic acid tobe completed.
A patent was taken out in 1873 by John Steed-man, of Glasgow , for a process for the purificationof acetic acid by passing the crude vapours throughsome hydrocarbon (preferably paraffin), kept at thetemperature of the distillate, in order to separate theempyreumatic matters before condensation. Theimpurities are retained by the hydrocarbon, and theacid vapour passes on in a pure state to ordinary con-densers, whilst the hydrocarbon is renewed periodi-cally as it becomes charged with the impurities.
The process may be practically carried out in anyconvenient vessel or apparatus, in which the crudeacetic acid vapours can be brought into intimate andcontinued contact with the purifying substance.Messrs. Steedman & M'Alister employ a coppervessel of a rectangular form, about 5 feet long, 1foot wide, and 2 feet 9 inches deep. This vessel isfitted internally with three partitions of copper orwood, which are horizontal in cross section, butslightly inclined longitudinally. The partitions areopen at alternate ends, and the vessel being filledwith paraffin, the acetic acid vapour, which is intro-duced from the usual distillatory apparatus by a pipeleading in beneath the closed end of the lowestpartition, travels along through the paraffin fromend to end beneath the partitions, and is finally ledfrom the top of the vessel to ordinary condensing ap-paratus. The paraffin is kept sufficiently heated by acoiled steam pipe, or steam jacket, or in any otherconvenient way, and is withdrawn from the vesselwhenever it is fully charged with impurities fromthe acetic acid. If wished, the acetic acid may bepassed successively through two or more vesselscontaining the purifying substances. In practice itis found to be convenient to use the “heavy oil”for the separation of the grosser impurities, and topass the acid afterwards through ordinary paraffinfor further purification. A purifying vessel of theabove dimensions is suitable for use in connectionwith a still of a size usually receiving about 100gallons at a charge.
A large portion of the impurities taken up by theparaffin may be separated therefrom by agitationwith hot water; and the paraffin may be furtherpurified by the processes ordinarily employed forthat purpose, and is then again fit for use as before.The heavy oil maybe purified by ordinary processes.
Of late years woody fibre has been much usedfor paper-making and analogous purposes; variouspatents have therefore been taken out, having fortheir object the extraction of the acetic acid,methylie alcohol, resin, &c., without carbonization :