The manufacture of white lead by this improved process requires oxides of lead and acetic acid, or acetates of lead and carbonic acid. ,,The oxides of lead are well known and abundant in the trade. Any oxide of lead, whatever is its preparation, which may be cheaply combined with carbonic acid, is satisfactory for this process. ,,Among the various oxides of lead found in the trade, litharge and massicot are the best for this operation. Red lead or minium does not suit at all. ,,The acetic acid employed should be free from coloring substances, which would discolor the white lead and impair its value. Acetic acid, free or already combined with oxide of lead, is used. The acid, as every chemist knows, may be obtained nearly colorless by the distillation of vinegar, or by the decomposition ,of the acetate of lime, or of any other combination of acetic acid with earthy, alkaline, or metallic bases. ,,It is not necessary to reproduce in this place the manner of effecting these decompositions, which is known to every manufacturer. Moreover, such an acetic acid is at the present day a product of the chemical trade. ,,"When acetate of lead is used, the neutral acetate or sugar of lead, and the basic solutions called Extract of Saturn and Goulard 9 s water, are employed. ,,Carbonic acid may be obtained by several methods actually in use ; but that which is preferred on account of its cheapness consists in collecting the gas resulting from the combustion of charcoal, coke, or anthracite. ,,In order to obtain a carbonic acid entirely satisfactory for the manufacture of good white lead, it is absolutely necessary that the fuels used should be entirely deprived of bituminous or volatile substances, that is to say, be nearly pure carbon with fixed substances (earths). ,,These materials are burned in a stove or oven, and the gases produced, which are a mixture of carbonic acid, nitrogen, and undecomposed air, are passed ,through a series of metallic pipes, so disposed in the air or in water, that the gases are cooled off to a moderate temperature. ,,In order to arrest any particles of unburt carbon, or any other substance which may injure the color of the white lead, the gases are passed through filters filled with irregular fragments of lead, such, for instance, as may be obtained by pouring the molten metal into cold water. ,,A small stream of water is allowed to percolate through the lead filters, which, therefore, are kept constantly wet during the passage of the gas, and aid considerably in its purification. When the presence of sulphur is suspected in the fuel employed, a small proportion of alkali is added to the water of the filters. ,Notwithstanding this precaution, it is better to be very particular in the choice of the fuel intended for the production of carbonic acid. ,,The carbonic acid already in the atmosphere could be employed for carbonating the oxide of lead, if its proportion were not so small. The operation would be so slow, that, in every respect, it is preferable to prepare carbonic acid by artificial means. ,,The following is the manner of manufacturing white lead with the above indicated materials: ,,If the oxide of lead is in big lumps, it is necessary to grind it down to a powder, which needs not to be so very fine. Litharge seldom requires this operation, and may be employed in the state in which it is bought. ,,The oxide of lead is mixed with the necessary proportion of acetic acid, or acetate of lead, and sufficient water is added to make a consistent paste. This paste is spread in thin layers over trays covered with sheet lead, and these trays are disposed one on top of the other in a room for the purpose, into which enters the carbonic acid, either pure, or mixed with other gases which cannot have any bad effects upon the beauty of the product. The carbonic acid is absorbed, and combines with the oxide of lead to make ceruse or white lead. ,,During the operation, the absorption is aided and rendered more rapid, by stirring with rakes the layers of lead, and thus presenting fresh surfaces to the action of the carbonic acid. ,,If the gas is dry, or does not carry with it sufficient dampness, a certain quantity of water is added to the mixture so as to render it more ready to absorb the ,carbonic acid. The proper degree is easily arrived at after several trials during the operation. ,,As the operation progresses, the oxide of lead, which was colored, becomes white; and when all of the mixture is free from colored parts, the treatment is finished, since all of the oxide has been transformed into carbonate. ,,The length of the operation varies with the proportion of acetic acid or of acetate employed, the rapidity of production of carbonic acid, and the attention ,given in stirring and in maintaining the proper degree of dampness. With the proportions of oxide of lead, acetic acid, or acetate, given further on, and a pro- ,duction of carbonic acid sufficiently rapid, and the proper care, the carbonatation requires from three to six days. ,,It has been found economical to mix at once part of the oxide of lead with the whole of the proportion of acetic acid or of acetate, and when this oxide is very nearly transformed into carbonate, to add a new proportion of oxide without any more acetic acid or acetate of lead. This new mixture, being exposed to ,the action of the carbonic acid, the free oxide is very rapidly converted into carbonate. A new proportion of oxide is again added, and the operation is continued ,as before, and always with a proper amount of moisture. ,,These successive additions of oxide are repeated (without more acetic acid or acetate) until the proportion of acetic acid or of acetate is reduced to onefourth, or even less, of that which was in the primitive mixture. ,,"When the carbonatation is finished, the mixture is spread in a stove-room, and allowed to dry. Then it is ground in a mill with water in the ordinary man- ,ner. The ground and floated product is dried again, and is white lead for painting and all other purposes. ,,The carbonated mixture may be ground immediately after its removal from the trays, without drying it first; but the latter operation improves the quality of ,the white. ,,For 100 kilogrammes of oxide of lead, we employ the same weight of a solution of acetic acid which contains 23 litres of No. 24 or proof vinegar. When we use acetate of lead, either solid or in solution, we take of either a quantity yielding the proportion of acetic acid just mentioned. ,