ACETIC ACID 13 



ucid. Christl 1 was therefore induced to employ hydrochloric acid as a decomposing 

 agent, and has found that when this acid is not used in excess, the distillate contains 

 scarcely an appreciable trace of chlorine. A mixture of 100 Ibs. of raw acetate of 

 lime, obtained from the distillation of wood, and containing 90 per cent, of neutral 

 acetate, with 120 Ibs. of hydrochloric acid (20 Baume) is allowed to stand during a 

 night, and then distilled in a copper vessel. The application of heat requires to be 

 gradual, in order to prevent the somewhat thick liquor from running over. The 

 product of acetic acid amounts to about 100 Ibs. of 8 B. ; it has a faint yellow 

 colour and empyreumatic odour, which may be perfectly removed by treatment with 

 wood charcoal and subsequent rectification. 



In order to obtain the acetate of lime sufficiently pure, Volckel z adopts the following 

 process : The raw pyroligneous acid is saturated with lime without previous distil- 

 lation. A part of the resinous substances dissolved in the acid are thus separated in 

 combination with lime. The solution of impure acetate of lime is allowed to stand 

 until it becomes clear, or it is filtered, then evaporated in an iron pan to about one- 

 half, and hydrochloric acid added until a drop of the cooled liquid distinctly reddens 

 litmus-paper. A part is sometimes distilled off in a copper still, in order to obtain 

 wood-spirit. The addition of acid serves to separate a great part of the resin still held 

 in solution, which collects together in the boiling liquid, and may be skimmed off, and 

 likewise decomposes the compounds of lime with creosote, and some other imperfectly- 

 known volatile substances which are driven off by further evaporation. As these 

 volatile substances have little or no action upon litmus-paper, its being reddened by 

 the liquor is a sign, that not only are the lime compounds of these substances decom- 

 posed, but also a small quantity of acetate of lime. The quantity of acid necessary 

 for this purpose varies, and depends upon the nature of the pyroligneous acid, which 

 is again dependent upon the quantity of the water in the wood from which it is 

 obtained. Three hundred pints of wood-liquor will require from 4 to 6 Ibs. of hydro- 

 chloric acid. 



The solution of acetate of lime is evaporated to dryness, and a tolerably strong heat 

 applied at last, in order to remove all volatile substances. Both operations may be 

 performed in the same iron pans ; but when the quantity of salt is large, the latter 

 may be more advantageously effected upon cast-iron plates. The drying of the salt 

 requires very great care, for the empyreumatic substances adhere very strongly to 

 the acetate of lime, as well as to the compound of resin and acetic acid mixed with it, 

 and when not perfectly separated, pass over with the acetic acid in the subsequent 

 distillation with an acid, communicating to it a disagreeable odour. The drying must 

 therefore be continued until, upon cooling, the acetate does not smell at all, or but 

 very slightly. It then has a dirty brown colour. The acetic acid is obtained by 

 distillation with hydrochloric acid, in a still with a copper head and leaden condenser ; 

 and when proper precautions are taken, the acetic acid does not contain a trace of 

 either metal. The quantity of hydrochloric acid required cannot be exactly stated, 

 because the acetate of lime is mixed with resin, and already formed chloride of 

 calcium. In most instances 90 or 95 parts by weight of acid, 1'16 specific gravity, 

 are sufficient to decompose completely 100 parts of the salt, without introducing much 

 hydrochloric acid into the distillate. 



The distilled acetic acid possesses only a very faint empyreumatic odour, very dif- 

 ferent from that of the raw pyroligneous acid ; it is perfectly colourless, and should 

 only become slightly turbid on the addition of nitrate of silver. If the acid has a 

 yellowish colour, this is owing to resin having been spirted over in the distillation, 

 It is therefore advisable to remove the resin, which is separated on the addition of 

 hydrochloric acid, and floats upon the surface of the liquid, either by skimming^ or 

 filtration through a linen cloth. The distilled acid has a specific gravity ranging 

 between 1'068 and-1'061, containing upwards of 40 per cent, of anhydrous acetic acid. 

 It is rarely that acid of this strength is required ; and as the distillation is easier when 

 the mixture is less concentrated, water may be added before or towards the end of the 

 distillation. Volckel recommends as convenient proportions 



100 parts of acetate of lime, 

 90 to 95 hydrochloric acid, 

 25 parts water, 



which yield from 95 to 100 parts of acetic acid of 1*105 specific gravity ; 150 litres 

 of raw pyroligneous acid yield about 50 IbSi of acetic acid of the above specific 

 gravity. 



The acid prepared in this way nlay be still further purified by adding a small 



1 Dingler's Polytcch. Joarn. * Ann, der Chcm. und Pharm. 



