The manufacture of mineral and lake pigments

by Josef Bersch

The air supply cannot be sufficiently regulated by the slides in the cover; these must be used in conjunction with the chimney damper. The combustion is observed through a thick glass plate let into the cover. At the commencement of the operation slides and damper are completely opened. When the chimney is seen to emit a thick black smoke the flues are filled with the products of combustion, and the speed with which they pass through the flues must be regulated. The current of air is decreased until only a little visible smoke escapes from the chimney, and the flame is no longer white, but a murky red. It should be noted that the first soot obtained from a new works is never of the best quality, the production of this is only gradually attained. The cause of this is that the new masonry is damp and gives up water to the hot gases, so that they are cooled and their velocity disturbed; the soot will also be damp. Thus a greasy soot is obtained. It is of very little use to allow the installation to remain unused for some months after it is completed; the brickwork would only dry superficially, and when it was first heated the presence of the water would become evident.

In order to dry the whole erection to such an extent that the moisture from the brickwork has no effect on the regular course of the operation, it is advisable to commence with materials of little value and to allow a portion of them to be lost by the use of a stronger draught than is generally used, so that the flues can be freed from all moisture as soon as possible. This applies equally to all kinds of arrangements for this purpose.

Fig. 31.

Lamps are used to burn liquid fats and mineral oils. These lamps naturally have a different construction to those used for lighting, which are constructed with the object of burning all the carbon in the oil, so that the temperature may rise as high as possible and the carbon burn at a high white heat. The lamps used in the soot black manufacture are designed to burn only as much carbon as is absolutely necessary to maintain the flame, at the same time the temperature of the flame must be kept low, so that no portion of the soot is again burnt. These lamps have flat burners and are enclosed in a sheet-iron casing provided with an air regulator, which must work very accurately, otherwise air will enter between the joints and the working of the regulator will be deceptive. So that the material to be burnt shall not be too strongly heated, which would be accompanied by great loss when mineral oil is used, the reservoir should be placed outside the iron casing which surrounds the burner.

[Fig. 31] shows the construction of a soot lamp. The flat burner, B, is placed in the cylindrical sheet-iron mantle, H, which is bent above at not too sharp an angle. The products of combustion are led into a chamber, K, from which they pass into the flues where the soot is deposited. The form of the upper portion of the cylinder is of importance; if this is bent at right angles, soot accumulates on the angle, and when a mass has formed it falls off, and is partly burned in the flame. If the cylinder is given a proper bend no soot is deposited in it, but it is all carried away into the soot chambers. The air regulator, S, is placed at the bottom of the cylinder; it must turn easily. The larger the slits are made by the rotation of this regulator, the more oxygen enters the flame, and the more vigorous is the combustion. A small, well-fitting door is placed in the lower part of the cylinder, through which the wick can be reached; opposite to this a glass plate is inserted, so that the flame may be observed without opening the door. The wick is raised or lowered by means of the screw, R.

The oil reservoir, O, must be outside the cylinder: in the older arrangements it is so placed that the wick sucks up the oil; the workman who is in charge of the lamps must then take particular care that the reservoirs always contain the proper quantity of oil, if he neglects to keep the oil at the proper level the wick is charred; it then sucks up too much oil, which cannot completely burn and is chiefly distilled, so that the soot is oily and cannot easily be treated afterwards. The most diligent and attentive workman who is in charge of a large number of lamps may easily allow one of them to run short of oil. With the oil reservoir above depicted, a new quantity of oil flows only when the level of the liquid sinks below the line, U. As soon as a small quantity is used air enters the reservoir, O, in place of which oil runs out until the opening, U, is again closed by the liquid. This construction of lamp only works well when thin oils are burned, and great care must be taken that the lamps are kept constantly clean.

Lamps of all constructions have some drawbacks, they must always be cleaned, and losses of oil occur in filling. These defects are obviated when, instead of providing each lamp with its own reservoir, a single one is used for a large number of lamps, which are automatically fed from it. In this case the attendant has only to regulate the air supply to the lamps, and to see that the mechanical arrangement by which the oil flows to the different lamps is working properly. When the lamps are automatically fed, the burners must be firmly fixed, and all in the same horizontal plane. A pipe connects each burner with a main pipe running under the lamps, which latter pipe is connected with the reservoir, and this in its turn is connected with another reservoir placed a little higher. In the pipe connecting the two reservoirs is a tap, which is opened by a float in the lower vessel as soon as the level of the liquid in it sinks a little, and which remains open until the level of the liquid has again risen to a certain height. The float in the reservoir connected with the lamps is arranged so that the level of the liquid is slightly higher than the burners. Under the slight pressure oil continually flows to the burners, and it is not difficult to regulate its flow so that all which reaches the burner is burned.

In using a new oil it is not easy at first to regulate the flow so that absolutely all is burned without any dropping off the burner; to prevent the loss of this portion, the lower end of the air regulator is conical, at the apex of the cone is a small tube and under this a vessel in which the unburnt oil is caught. In [Fig. 32], S is the air regulator, T the vessel to catch the unburnt oil, L the pipe leading from each burner to the common pipe H, G the vessel in which a float regulates the flow from a larger reservoir, so that the liquid always remains at the same level. When tar oils are used, or thin mineral oils, the pipes which convey the oil to the burners may be made tolerably narrow, but when viscous oils or fish oils are burned, narrow tubes would offer too great resistance to the flow, so that it is always advisable to use fairly wide pipes. Viscous oils become considerably more fluid at higher temperatures, it is therefore well to place the reservoirs in the same room as the lamps; in winter the temperature of this room is kept fairly high by the burning of the lamps, and thus the oils remain fluid.