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and then ammonium oxalate, and the beaker-glassplaced on the sand-bath. When the lime oxalatehas subsided, it is collected, washed with water,dried as the preceding precipitates, and burned in aplatinum crucible. The ignition should be gentle,and at a heat very little above dull redness, so asnot to expel carbonic acid from the carbonate oflime, which is formed by the action of the heaton the lime oxalate, as is shown in the annexeddecomposition:—
Calcium oxalate. Calcium carbonate. Carbonic oxide.
CaC 2 0 4 = Ca(J0 3 + CO
The weight of the carbonate of lime obtained isequal to the amount of that adulterant which hasbeen added to the verdigris.
Verdigris generally contains about 3 per cent, ofimpurities. Sometimes the insoluble matter in it is6 per cent.; in such a case, however, the article isof inferior quality.
Formerly the manufacture of verdigris was oneof the most lucrative in Belgium , and it was alsocarried on profitably in France ; but at the presenttime the production of this substance is not con-fined to those countries. France still producesconsiderable quantities of the article, and nearlythe whole of the salt imported into this kingdom isfrom that country. Until the 19th of March, 1845,the duty on verdigris imported into this countrywas ls'jyd. per lb. weight ; it was then subjected toan ad valorem duty of 10 per cent., which was re-pealed in 1853. The imports are neverthelesssmall, as large quantities of verdigris are preparedin England with pyroligneous acid and cider refuse.
Iron Acetates. —There are two acetates of iron,ferrous acetate and ferric acetate.
Ferrous Acetate, Fe (C 2 II 3 0 2 ) 2 .—This salt may beprepared by dissolving either iron sulphide ormetallic iron (generally iron turnings are used) instrong acetic acid; in the former case sulphurettedhydrogen,'in the.latter gaseous hydrogen, is evolved.
Ferrous'sulphide. Acetic acid. Ferrous acetate. Sulphydric acid.
FeS + 2C 2 Il40 2 — Fc{C 2 H 3 0 2 ) 2 +
Acetic acid. Ferrous acetate.
Fe + 2(l a H 1 0 2 = F e (C 2 H 3 0j 2 + 2H.
On concentrating the solution, small colourless silkyprismatic needles are obtained, which are verysoluble in water, and which, when exposed to theair, rapidly absorb oxygen, and become convertedinto. ferric acetate. This compound may likewisebe obtained by decomposing a solution of the fer-rous sulphate (green vitriol, FeS0 4 ) by calcium orlead acetate: 1615 parts of ferrous sulphate require2575 parts of lead acetate, or 999 parts of calciumacetate ; but in this method a greater or less amountof ferric acetate is also formed, which can, however,be reduced to the state of ferrous acetate by passinga stream of sulphuretted hydrogen gas through theliquid.
The avidity with which this substance absorbsoxygen renders it of groat value as a reducingagent.
For commercial purposes this compound is manu-factured as follows:—Into a large cast-iron boiler orpot a quantity of iron turnings, hoops, or nails areintroduced, and acetic acid—the crude pyroligneousacid from the distillation of wood—is poured inupon them. The strength of the acid is generallyof 7° Twaddle, or spec. grav. 1'085. A temperatureof 150° Falir. (66° C.) is maintained till the solution offerrous acetate is obtained, of a spec. grav. 1-09, or18°T., at 60°Fahr. (15° C.). During the solution of theiron much tarry matter separates, which is skimmedoff, and the solution frequently agitated, to free itas much as possible from the tar. As soon as theabove strength is gained the solution is allowed tocool, for a further quantity of impurities to separate.When clean turnings are operated upon, the processof solution is completed in five to seven days. Thehydrogen that is eliminated during the solution ofthe iron prevents the oxidation of the iron salt, asis seen in the equation already given. Were anyferric acetate formed, the hydrogen, by combiningwith part of its oxygen, would again reconvert it toferrous acetate.
Some printers dissolve the iron without the aid ofheat, but this method is slow and unsatisfactory, forthe deposit of tarry bodies on the iron prevents theaction of the acetic acid ; besides, from the long ex-posure to the air, some sesquisalt of iron is generated.The usual produce from 100 gallons of acetic acid,and a proportionate quantity of iron turnings, is 60to 70 gallons of acetate of iron, spec. grav. 1-090, or18° T.; and when this solution is reduced by theaddition of water to a spec. grav. 1-060, it produceswith madder a deep black.
The mordant is likewise made by decomposing asolution of sulphate of iron (FeS0 4 ) by acetate oflime; the proportions employed are the following:—
400 lbs. of sulphate of iron—copperas—dissolved in
100 gallons of hot water, ami the solution decomposed in
75 gallons of acetate of lime liquor, spec. grav. 1-08.
On agitating the mixture, the decomposition is ren-dered complete ; the clear liquor, which is siphonedoff after subsidence of the sulphate of lime, pos-sesses a density of 1-110.
When the liquor is not required for immediateuse it becomes oxidized, and deposits ferric acetate;to prevent this some metallic iron is left in contactwith the solution. Sometimes, when a large quan-tity of pyroligneous matters deposits in the solution,the iron is prevented from acting by becoming coatedwith these substances; in such instances the for-mation of the basic acetate may be prevented bysuspending fine iron wire in the liquid.
In some of the continental factories the ferrousacetate is manufactured by decomposing the car-bonate of iron (ferrous carbonate, FeCO s ) with leadacetate: lead carbonate precipitates, and the black-ish supernatant liquor is the acetate of iron in avery pure state. It is kept from oxidizing by im-mersing in it some bright iron filings. The lead-salt formed repays the cost of the manufacture ofthe acetate.