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matter, &c., in the acetate of lime, is harmless, pro-vided that the salt has been sufficiently heated todrive off the free volatile substances. When, on thecontrary, sulphuric acid is used, the acetic acid pro-duced has always a bad odour, is saturated withsulphurous acid, and contaminated by a variety ofproducts arising from the deportment of the resinsat an elevated temperature. The sulphate of limeproduced also forms a hard crust at the bottom ofthe retort, and in distilling on the large scale theunder part of the alembic must be heated completelyto redness to drive out all the acetic acid. The lastportions of acid that pass over are moreover oftenturbij from sulphur, and the odour of sulphurettedhydrogen becomes perceptible, that gas arising fromreduction of the sulphate of lime to sulphide of cal-cium at the bottom of the vessel; from these causesthe cast-iron x’etorts soon become corroded.
Pure acetic acid may be obtained by the methodabove described at so very low price that it may beadvantageously used in the preparation of acetates,es peeially of acetate of lead.
■^n important improvement in the purification ofacetic acid was patented by II. 15. Condy in 18C8.It has long been known that a solution of acetateand chloride of calcium, in equivalent proportions,yields by slow evaporation large crystals containingCaCl,CaC 2 H 3 0 3 + 511,0, calcium aceto - chloride.
II. Condy has found’that, by judicious manipula-I’°n, these crystals are readily formed, and in a state°I great purity, even when black and brown acetateof lime is operated on. From the pure double salthe obtains pure acetic acid by adding to it a strongacid and distilling.
I or the manufacture of the calcium accto-cldoride°r the subsequent manufacture of pure acetic acid,any inferior acid, such as that obtained by the dis-tillation of commercial acetate of lime with sulphuric I°i muriatic acids, may be employed; but the mostpractical and economical plan is to take 8 cwts. ofcommercial acetate of lime, known as distilled acetate°I Ihne, and dissolve it by boiling in 500 gallons ofwater. This is filtered or allowed to settle till the“°xt day, when a quantity of dry chloride of calcium,w lual in weight to seven-tenths of the acetate of limeemployed, is dissolved in it by beat and agitation.
commercial chloride of calcium, or a strong solu-1011 °f chloride of calcium, is used, it is necessary0 take into calculation the water present, and toe mploy an additional quantity of chloride in coni-on ' This mixed solution of acetate and0 1 oride of calcium, containing, in addition to theTmntity necessary to form the aceto-chloride, anexcess of about 20 per cent, of chloride, is broughty careful management when boiling hot, or nearlythe specific gravity of 30° Beaume ; if it should® of a lower specific gravity it is evaporated to thiss rength; if it he too strong it is diluted to the samepoint, and then drawn off to crystallize. When?.° an d a crop of salt (aceto-chloride) has crystal-led out,, the mother liquor is drawn off and eva-perated down till the hot liquor shows a strength of
These evaporations and crystallizations are repeateduntil three other crops of aceto-chloride are obtained.For the third crop the liquor drawn off boils atabout 33° Beaume, for the fourth at aBout 35°Beaume, and for the fifth about 3(i° Beaume. Thesefive crops are of tolerably uniform quality, andleave by' far the greater part of empyreumaticmatter in the last mother liquor, which lias givenup nearly all its valuable and available acetate inthe form of crystal, and is then either rejected, orit may be distilled with sulphuric or hydrochloricacid for producing an inferior acetic acid.
For manufacture of the pure salt these five crojis,after they have been well washed and drained, areredissolved in twice their weight of water, the solu-tion filtered through animal charcoal, and a furtherquantity of 10 per cent, or thereabout of chloride ofcalcium is added, after which the liquor is evapo-rated to 29° Beaume, at which strength a good cropof white salt is obtained. The mother liquors fromthis salt are again evaporated down, and the hotliquor drawn off to crystallize at 30° Beaumd toobtain a second crop, at 31° for a third crop, andat 32° for a fourth crop. The mother liquor is thenturned into the original solution of calcium aceto-chloride, from which the first of the five crops ofrougli salt referred to lias been obtained.
Commercial brown acetate of lime, or even crudepyroligneous acid, may be employed for this process,but not with the same advantage. In the case ofbrown acetate of lime, it is necessary to observethat the weight of acetate of lime employed shouldbe 20 per cent, more than that of “ distilled ” for agiven weight of chloride of calcium, i.e., about 12parts brown acetate to 7 parts dry chloride; thatthe specific gravity of the liquor drawn off forobtaining each crop of salt (aceto-chloride) must boadjusted or regulated by experiment, since no twosamples of brown acetate of lime are quite alike, andthat it will depend in each case on the care withwhich the acetate may have been prejiared. Thiscan be ascertained during the process of evapora-tion by cooling and crystallizing a sample, after theboiling or hot liquor has attained 30° Beaume. Ifafter cooling a good crojj of salt is not obtained, theliquor must be evaporated further until that objectis accomplished. To obtain this salt by the employ-ment of crude pyroligneous acid it is necessary toneutralize with lime, and to estimate the quantityof dry brown acetate it contains by evaporating asmall portion to dryness and weighing the product.
If the solution contains 1 part of brown acetatein 10 parts it will be simply necessary to bear inmind that 12 parts of the dry acetate in it require7 parts of chloride of calcium, and that for thefirst crop it must be evaporated to 32° Beaume; thetendency to crystallize must then be estimated by-taking out a hot sample and allowing it to cool, andagain evaporating until the required strength forcrystallization is obtained. As a rule the motherliquors in all cases require to be evaporated to halftheir bulk to yield a further crop of salt, and thenthe tendency to crystallize can be ascertained.