THE

London

JOURNAL AND REPERTORY

OF

Arts, Sciences, and Manufactures.

CONJOINED SERIES.

No. XCI.

Recent Patents.

To THOMAS ROBERT SEWELL, of Carrington, in the parish of Basford and county of Nottingham, lace manufacturer, for his invention of certain improvements in the manufacture of white lead.-[Sealed 11th January, 1837.]

THESE improvements in the manufacture of white lead consist, in the first place, in a mode of combining oxygen with lead, by the agency of the combustion of charcoal, for the purpose of producing a material or substance, commonly called or known to chemists as protoxide of lead, in connection with a mode of preserving and applying the carbonic acid gas, generated by the combustion, to the further purpose of carbonating protoxide of lead. Secondly, in certain improved modes of operating for the purpose of carbonating protoxide of lead, in order to produce the substance or pigment, called ceruse or the white lead of com

VOL. XV.

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merce. Thirdly,-in the construction and arrangement of apparatus suited to perform one or both of these operations separately or combined.

As respects the first head of my invention, I place metallic or blue lead in a suitable receptacle, where it is melted by the heated gases produced from the combustion of charcoal, and oxydized by the oxygen of the undecomposed atmospheric air brought over its surface; by means of which operations the lead becomes oxydized, and rendered in a fit state for being converted into the pigment called white lead; and the carbonic acid gas, instead of being allowed to escape into the atmosphere, immediately after passing over the lead, is conducted through pipes, by means of a pump, to the vessel in which the carbonating process is to be performed.

As to the second head of the invention, I place protoxide of lead, prepared as above, and ground and washed (or by any other process which may have rendered it fit for the purpose) in a suitable vessel, containing a solution of acetate of lead, or of acetic acid, or any other suitable solvent of protoxide of lead, and pass through this mixture a current of carbonic acid gas, for the purpose of agitating the mixture, and promoting the action of the solvent upon the oxyde; and when a portion of the oxyde has become dissolved in the solvent, causing the carbonic acid gas to unite with it, and to precipitate ceruse or white lead.

The third head of the invention-the construction and arrangement of apparatus suited to purposes of the above operations-will be best understood by reference to the accompanying drawings, in which fig. 1, Plate I. is a longitudinal section of an apparatus, arranged to conduct the operation from the beginning to the end.

A furnace a, containing a quantity of ignited charcoal, is placed contiguous to a vessel or trough b, b, formed of

fire-brick, which is shown in transverse section at fig. 2. This vessel contains a quantity of metallic or blue lead c, and is covered by a roof d, d, of fire-brick, forming a very narrow channel as a flue over the surface of the lead. The furnace is supplied with atmospheric air from the open ashpit e, below, and the oxygen and other gases, as well as the carbonic acid gas, generated from the combustion, pass in a heated state through the vessel b, over the surface of the lead, and in passing cause the lead to melt. A quantity of cold air may be admitted, if necessary, at the door f, in front, for the purpose of regulating the temperature of the melted lead, which should be kept at a low red heat during the operation.

g, car

In the passage of the gases over the surface of the melted lead c, oxygen enters into combination with the lead, and converts it into an oxyde. The carbonic acid and other gases, proceeding onward, descend into the chamber rying with them the oxyde thus produced, which deposits on the floor, at the bottom of the chamber, (and from thence may be removed when necessary, by opening the door h,) whilst the gases pass up through the pipe i, i.

It will now be necessary to show the means by which I produce a current of air and gases through the furnace a, the lead vessel b, the chamber g, and the pipe i, i, i.

A tank of water is fixed in the masonry at k, k, and in this is placed an inverted vessel l, l, supported by bars m. A perforated diaphragm n, n, is fixed within this vessel, which diaphragm may be covered with a sheet of wire gauze, for the purpose of causing the gases, which are to be passed through the diaphragm, to be separated into very minute bubbles. Pure water is delivered into the vessels 7 and k, by a pipe from a cistern o, which may continue flowing until the tank k is filled nearly up to its brim. A wooden vessel p, p, p, (say about six feet diameter and six

feet deep,) is furnished with a false bottom of wood 9, which is perforated with holes, each of about an inch in diameter. This false bottom is placed a few inches from the real bottom, forming a space, between them for the introduction of the gases. Upon the upper surface of the false bottom, a sheet or diaphragm of very closely woven canvass, or wash leather, or other suitable porous substance, is tightly distended, and secured in that situation; or, perhaps, a false bottom of porous wood might answer the purOn this diaphragm I place a quantity of protoxide of lead, say a ton weight, and then nearly fill the vessel p with a solution, consisting of about nine hundred weight of acetate of lead, dissolved in about four or five times its weight of water; which solution is intended as a menstruum for dissolving the protoxide of lead, and becomes the vehicle for the chemical operation which is to follow; or, instead of this solution, acetic acid, or any other suitable solution of lead, may be employed, but I prefer that above mentioned.

pose.

Now in order to carry on the process of making white lead by the apparatus under consideration, I employ an air pump r, which is connected by pipes and chambers to the furnace a, on one side, and to the vessel p, on the other side, as represented partly in section in fig. 1. A pipe s, s, s, leading from the upper part of the vessel l, is connected to the induction side of the air pump, and a pipe t, from the eduction side, leads into a close air tight vessel u, furnished with a weighted valve, to regulate the pressure within.— From this vessel u, a pipe v, having a regulating stop cock, communicates with the compartment, under the false bottom g, in the vessel p. The air pump r, which is constructed on the double-action principle, is to be worked by a steam engine, or other adequate means, applied to its piston, by the action of which the atmospheric air is drawn