We now pass to the details of the operation by the Holland process, with various abservations and comparisons made in several French works, by Mr. R. Combes, and reported by him to the Academy of Sciences.,The Holland or Dutch process comprises the following operations:-,1st. Fusion and casting of the lead in sheets of variable thicknesses, or into rectangular or round grates (buckles).,2d. Alternate layers made of lead and stable manure, or spent tan. The lead is put into pots holding weak acetic acid, and remains in the beds from 35 to 40 days when stable manure is employed, and from 70 to 90 days when spent tan is used.,3d. Successive uncovering of the layers of lead, the greater part of which has become carbonate. Separation of the white lead from the non-corroded metal. First grinding and separation of the blue lead.,4th. Grinding the white lead with water under stones.,5th. Moulding and drying the floated white lead.,6th. Grinding and sifting the dry white lead, and packing in barrels that which is to be sold powdered. ,7th. The white lead which is to be made into paste with oil is not sifted, but mixed with from 7 to 10 per cent. of its weight of oil. The mixture is effected in a closed stirrer, and then passed between a series of horizontal cast-iron rollers. When the paste has become fine and homogeneous, it is received in a tank filled with water, from which it is taken and packed for sale. ,I. The fusion of the lead is effected in cast-iron kettles, and no dangerous fumes are emitted unless old lead or the residues of previous operations, still covered with carbonate, are melted. In well-disposed works, [65] the kettle is placed under a hood receiving its draft either from the chimney flue of the furnace itself, or from another stack with a good draft. The top edge of the furnace is connected with the hood by means of a metalic prism or cylinder, having doors which are open for charging the lead, or for casting into moulds the fused metal. These precautions seem to us sufficient for protecting the men from the noxious fumes. Moreover, the fusion of the lead is intermittent.,II. The forming of the layers of lead and stable manure or spent tan, presents no danger. The buckles or the thin sheets of lead rolled into spirals, are put into earthenware pots, and there supported upon two or three projections. The vinegar is at the bottom of the pot.,III. The separation of the white lead from the non-corroded metal, and the first dry pounding and sifting are the most unwholesome parts of the manufacture. In nearly all of the works of Paris, the workman picks up by hand the large and slightly adhering scales of white lead, and separates the remainder by twisting and bending in every direction the non-corroded lead. This hand picking is generally done in the bed itself, and sometimes in a special room where the whole of the corroded metal is carried, in the shape it comes from the pots.,This picking, however, where the hands are constantly covered with carbonate of lead, is not the most dangerous part of the operation, because the thick [66] scales are separated without much dust. But as the metallic lead retains a certain quantity of white lead strongly adhering, it was formerly beaten with a wooden rammer, thus producing a fine dust, which was inhaled by the workman. This operation is therefore the most dangerous, and is now substituted in several works by mechanical means which imperil the health of the men much less. The buckles or sheets with their still adherent white lead are put, one by one, upon an endless cloth, which carries them to an inclined hopper, from which they pass between two pairs of grooved rollers, and thence through an inclined cylindrical sieve. What passes through the holes of the sieve is received into a hopper, which delivers it into a trough on wheels. The metallic lead falls from the lower opening of the sieve into another trough. The whole of the machinery is inclosed in tight wooden partitions, the only free opening of which is that for the passage of the endless cloth. The trough filled with white lead is removed when the dust has subsided, and its contents are mixed with the scales picked up by hand.,The next dry grinding is, in the majority of cases still effected under vertical zones, rolling upon a horizontal bed. The ground lead is then shovelled into a cylindrical metallic sieve with fine holes, and inclosed in a wooden box. The powdered white lead is collected at the bottom of the box, and the small flattened particles of metallic lead, fall from the lower end of the sieve into a specail receiver. The sifted white lead is mixed with water, and thoroughly ground under mill-stones.,In several manufactories in the neighborhood of Lille, the scales of white lead are powdered between [67] several pairs of horizontal grooved rollers. The divided substances fall upon one or several metallic sieves, and from them in to hoppers which conduct them to a receiving trough, where they are moistened with a spray of water. The metallic lead falls into a separate room. The whole of the grinding rollers and sieves occupy the height of a story, and are inclosed in wooden partitions. The upper hopper is kept filled with the scales of white lead, so as to prevent the escape of dust. Moreover it may be entirely closed with a trap door. These dispositions are a great hygienic improvement on the old process of manufacture. ,In those works of the department of the Seine, where the lead is cast into grates or buckles, and not into sheets, the separation of the white lead and its dry pulverization and sifting are effected by mechanical apparatus following one another, and placed in closed rooms.,The first room contains a series of three pairs of grooved rollers which separate the white lead from the non-corroded metal, and another series of three pairs of smooth rollers which grind the scales of white lead. There is an opening at each opposite extremity of the room: one for the passage of the endless cloth carrying the corroded buckles; and the other for the escape of the cleaned lead which slides upon a sheet-iron apron, perforated with holes and made to shake by machinery. These grates or buckles of metallic lead are received by one or two workmen, who put apart the thin ones for remelting, and separate and straighten those which are thick enough to go into the beds again.,The scales of white lead, separated by the grooved [68] rollers, fall upon an endless cloth placed under the shaking apron of perforated sheet iron, and are brought upon the three pairs of smooth rollers, between which they are powdered. The powder falls upon an inclined plane which conducts it to pit, from which it is taken up by an endless bucket strap (inclosed in tight wooden troughs), and carried to the top of an upper room, where the metallic sieve for the separation of the blue from the white lead is. The metallic portions are received in a distinct place, and the whitelead falls on to the floor of the room, from which it is removed when the dust has settled. In this operation, the men who receive the buckles of lead from the rollers, are still exposed to the dust of the white lead, and remain but a few days at that work.,To sum up: the separation of the scales of white lead, and their dry grinding and sifting, cannot be considered a wholesome manufacture anywhere, although there have been many improvements made and hygienic precautions taken in most of the works we have visited. Certain manufacturers have tried to obviate the not very great danger of picking white lead with the hand, by furnishing the men with gloves. This precaution seems to us insufficient, because gloves are often an impediment to the work, and the men will be tempted to leave them off.,In the works where the separation of the white lead from the non-corroded metal is not done by hand, there is still danger of inhaling fine white lead dust, when the thick buckles are straightened and struck with the mallet. Lastly, a very fine lead dust escapes from the rooms containing the grinding apparatus, either from the apertures for the inlet or [69] outlet of the substances, or from the openings cut in the wooden partitions for the passage of the shafting. ,The causes of danger would quite cease to exist, if the separation of the scales of white lead, their grinding and sifting, were effected under water; or, at least, if the white lead and the metallic residues were subjected to sprays of water immediately after they leave the grinding apparatus. Such is the mode of operation, as we learn from data of Mr. Le Play, in the English white lead works. There, all the metallic residues are cast anew, before returning to the beds. We call the attention of manufacturers and of the public administration to this method, which presents no serious difficulties, since it is generally practised in England. The white lead is also deprived, by washing, of certain soluble salts which may injure its purity; moreover the subsequent operation is always effected with the aid of water.,IV. The white lead is mixed with water in troughs, so as to form a soft paste which passes successively through several horizontal mill-stones before it is thoroughly comminuted. This wet grinding is absolutely without danger, since the men do not touch the white lead with their hands, but carry it in scoops or ladles.,V. In all the works which we have visited, the soft paste of white lead is poured into conical earthenware pots, which are dried in a stove room.The greater part of the water is expelled, and the blocks becoming contracted, are easily removed from the pots. Their thorough drying is finished in another, or the same, stove room.,The sides of the pots are coated with white lead, which is generally scraped off with an iron tool. This [70] operation is performed by women or children, and is not without inconvenience. It is remedied in certain works, by washing the pots in water; but this involves more labor and expense. Part of the white lead is sold, after drying, in the shape of conical blocks, which are wrapped in paper and put into barrels, care being taken not to break them. This handling of white lead is not entirely wholesome, although, with the proper precautions, it is not dangerous.,In an establishment of the department of the Seine, the white lead is not put into pots; but the soft paste is poured upon a cloth which is then folded so as to form a square flat bag. Several such bags, separated by square wooden trays, are afterwards squeezed in a hydraulic press, which expels the greater part of the water. After unfolding the cloth, the block of white lead is cut into prisms or bricks having sufficient consistency to be carried immediately into the dryingroom. A small proportion of the product of these works is sold in the shape of dry prisms: but their packing in barrels is not done with the same care as with the conical blocks, because the products go to consumers sufficiently learned to know that the external shape of white lead is no proof of its good or bad quality. The bricks or prisms of white lead are compressed in the barrel by the cylinder of a hydraulic press.,VI. The greater part of the white lead in lumps requires to be ground and sifted again before it is ready for sale. This second grinding, in the majority of works, is still done with vertical stones rolling upon a sstone bed. The ground stuff is shovelled into the hopper of a cylindrical solk sieve, inclosed in a [71] wooden box, where the fine white lead falls. That which has not passed through the meshes of the sieve is collected in another box, and ground anew. The sifted white lead is removed from its box, after the dust has subsided, and packed in barrels either by shaking, or by a slight ramming.,The grinding, sifting, and packing of the dry white lead by the foregoing method, are evidently dangerous on account of the dust floating in the workshop. The inconveniences can be considerably diminished, by inclosing within wooden partitions the mill-stones and the sieve, as is practised in lead works at Lille, where the vertical stones have been replaced by horizontal ones of white marble. Each pair of stones is within a drum, on top of which is a hopper filled with the lumps of white lead, coarsely broken by means of a rotary grooved cone placed within it. The powdered material is, by centrifugal force, projected against the drum, and falls by two diametral openings into the sieve below, which is also well inclosed. In order to prevent the dust from flying during packing, the white lead is compressed by means of a wooden disk, of nearly the same diameter as that of the barrel, and pressed downwards by a screw.,VII. The works in the neighborhood of Lille sell the greater part of their products in the shape of powder or lumps: that is, about one-third in lumps and two-thirds in powder. a manufacturer of the department of the Seine has all the apparatus necessary for grinding the white lead in oil, and seven-eights of his production is sold as paste holding from 7 to 9 pre cent of oil. The prisms of white lead are ground in a kind of coffee mill, which delivers a not very fine powder. The powder is then put into a horizontal [72] cylinder, with a certain proportion of oil, and mixed by means of iron paddles fixed to the shaft running the length of the cylinder. From thence the paste passes between a series of cast-iron rollers, and becomes fine and homogeneous. More oil is added if necessary. The finish paste is kept under water in large tubs, from whence it is taken for packing.,Thus, when white lead is ground in oil in good apparatus, like those we have seen in operation, it is not necessary to grind it into a fine powder, and we avoid one of the most unwholesome operations. It is therefore highly advantageous that all the white lead (and we believe that by far the greater part of the white lead is always ground in oil) should be mixed with oil in the works themselves, instead of in many separate shops, where the men are subject to lead colics, from want of proper precautions and apparatus. It appears certain, from what we have seen in a leadworks at Birmingham, and from the data of Mr. Le Play, that the English manufacturies deliver the greater part of their products in the shape of a paste holding from 8 to 9 per cent of oil.* It is highly desirable that the same thing should be done in France.,,* In England, at least in several works, there are three brands of white lead paste; the first is pure white lead with from 8 to 9 per cent. of oil; the other two qualities contain sulphate of baryta in the proportions of about 15 and 25 per cent.