_a_ is a vat, which may be made of wood or other material capable of resisting the chemicals employed; it may conveniently be 6 feet in diameter and 4 feet deep, and it is provided with a closely fitting cover, _b_ is a cistern situate at a higher level, and intended to contain a solution of acetate of ammonia, _c_ is a pipe by which the solution can be drawn down from the cistern _b_ into the vat _a_; a cock is provided upon this pipe, as the drawing indicates. There is a man-hole _d_ in the cover of the vat, and the vat contains an agitator _e_, with a vertical shaft which can be turned by gearing _f_ as shown, or the agitator may be driven by any suitable motor. The shaft of the agitator _e_ is hollow, and pipes _g_, which stand immediately behind the stirring tines, are connected with the hollow shaft, to deliver the carbonic acid gas into the vat; or this may be effected by means of coils of pipe laid at the bottom of the vat, and pierced with small holes. The pipes _g_ are open at their lower ends. _h_ is a cock by which the liquor can be drawn off from the vat into the receiver _i_. A pump _k_ is provided upon the cover of the receiver, by which the liquor may be returned into the vat _a_. _l_ are outlets by which the white lead is discharged from the [Illustration: Fig. 26.--MACIVOR’S WHITE LEAD PLANT.] vat into the washing cisterns _m_ and _n_. _o_ is a man-hole, which may be opened to facilitate the emptying of the vat. _p_ is a plug which is removed to let the white lead run out of the vat. _r_ is an ammonia catch box, charged with acetic acid. All the metal-work of the apparatus with which the acetate solution comes into contact should be of such a character as to resist corrosion, or should be coated with a material capable of withstanding attack by the chemicals employed in or formed during the process. The operation is by preference conducted in the following manner, but the details admit of variation. The charge of monoxide of lead for an apparatus of the dimensions indicated may weigh about 1120 lb. The monoxide should be in fine powder, and may be either moist or dry. Having received this charge, which is introduced by the upper man-hole _d_, the vat _a_ is closed, and a solution of acetate of ammonia is let down upon the charge from the cistern _b_, or pumped out of the receiver _i_. The vat _a_ should be charged with the solution of acetate of ammonia in the proportion of three parts of said solution to one part of lead monoxide by weight. It is convenient to employ a solution containing 5 per cent. of acetate of ammonia, and the quantities above stated are suited to a solution of this strength; but the strength of the acetate solution may be varied within wide limits, as hereafter explained.