952 SUINT 



with heat, in strong vinegar, made of malt, wood, or wine, till the acid be satu- 

 rated. A copper boiler, rendered negatively electrical by soldering a strap of lead 

 \rithin it, is the best adapted to this process on the great scale. 325 parts of finely 

 ground and silted oxide of lead require 575 parts of strong acetic acid, of spec. grav. 

 7 Beaume", for neutralisation, and afford 960 parts of crystallised sugar of lead. 

 The oxide should be gradually sprinkled into the moderately hot vinegar, with con- 

 stant stirring, to prevent adhesion to the bottom ; and when the proper quantity is 

 dissolved, the solution may be weakened with some of the washings of a preceding 

 process, to dilute the acetate, after which the whole should be heated to the boiling 

 point, and allowed to cool slowly in order to settle. The limpid solution is to be 

 drawn off by a syphon, concentrated by boiling to the density of 32 B., taking care 

 that there be always a faint excess of acid, to prevent the possibility of any basic salt 

 being formed, which would interfere with the formation of regular crystals. Should 

 the concentrated liquor be coloured, it may be whitened by filtration through granular 

 bone-black. 



Stoneware vessels, with salt-glaze, answer best for crystallisors. Their edges 

 should be smeared with candle-grease, to prevent the salt creeping over them by 

 efflorescent vegetation. The crystals are to bo drained, and dried in a stove-room 

 very slightly heated. It deserves remark, that linen, mats, wood, and paper, imbued 

 with sugar of lead, and strongly dried, readily take fire, and burn away like tinder. 

 "When the mother-waters cease to afford good crystals, they should be decomposed by 

 carbonate of soda, or by lime skilfully applied, when a carbonate or an oxide will be 

 obtained, fit for treating with fresh vinegar. The supernatant acetate of soda may 

 be employed for the extraction of pure acetic acid. 



A main point in the preparation of sugar of lead is to use a strong acid ; otherwise 

 much time and acid are wasted in concentrating the solution. This salt crystallises 

 in colourless, transparent, four- and six-sided prisms, from a moderately concentrated 

 solution ; but from a stronger solution, in small needles, which have a yellow cast if 

 the acid has been slightly impure. It has no smell, a sweetish astringent metallic 

 taste, a specific gravity of 2'345 ; it effloresces slightly in a dry atmosphere, and when 

 heated above 212 Fahr.it froths up and loses all its water of crystallisation, together 

 with some acetic acid, falling into a powder which passes slowly in the air into car- 

 bonate of lead. If heated to 536 Fahr. it is entirely liquid, and at a higher temperature 

 is decomposed, disengaging acetic and carbonic acids, and some acetone ; the residue 

 consisting of very finely divided and very combustible metallic lead. The crystals of 

 acetate of lead dissolve in 1 time their weight of water at 60 Fahr., but in much less 

 of boiling water, and in 8 parts of alcohol. The solution feebly reddens litmus-paper, 

 although it imparts a green colour to syrup of violets. The constituents of the 

 normal salt are. 5871 oxide of lead, 27'08 acetic acid, and 14'21 water, in 100, or 

 PbO.C'H'O 3 + 3HO [Pb (C=H'0 2 ) 2 + 3K-O]. 



Acetate of lead is much used in calico-printing. It is poisonous, and ought to be 

 prepared and handled with attention to this circumstance. 



Four subacetates of lead are generally acknowledged to exist, viz. : 



Sesquibasic acetate. This is obtained by heating the neutral acetate in a capsule till 

 tho fused mass becomes white and porous ; this is then dissolved in water and evapo- 

 rated, when on cooling pearly laminae separate ; they are soluble in water and alcohol, 

 and the solution possesses an alkaline reaction. 



Dibasic acetate. This salt, when in solution, is known as Goulard's extract, and is 

 formed by boiling together a solution of the neutral acetate and an equivalent quan- 

 tity of pure litharge (oxide of lead). In the solid state it is crystalline. 



Tribasic acetate. This salt is the most stable of the subsalts. It is obtained in the 

 crystalline state, by leaving to itself a cold saturated solution of the neutral acetate, 

 to which one-fifth of its volume of caustic ammonia has been added. It may also 

 bo made by digesting 7 parts of pure litharge with a solution containing 6 parts of 

 the crystallised neutral acetate. It forms long silky needles, which are very soluble 

 in water, but insoluble in alcohol.' Carbonic acid transmitted through the solution 

 precipitates the excess of oxide of lead, in the state of carbonate ; a process long since 

 described by Thenard, for making white lead. 



Hcxbatsic acetate. This subsalt is obtained by boiling any of the other acetates 

 with an excess of litharge. It is a precipitate, which, when examined by the micro- 

 scope, presents a crystalline aspect. It is slightly . soluble in boiling water, from 

 which, in cooling, white silky needles are deposited. This salt is frequently found 

 in commercial white lead. The solutions of subacetates are rapidly decomposed by 

 the carbonic acid of the atmosphere. 



StTOTT. Quite a recent instance of improved economy is found in the treatment 

 .of the wool of sheep. It has been ascertained that sheep derive from tho soil upon 

 which they pasture a considerable amount of potash, which, after it has circulated iu 



