The only method which has met with even partial success is that adopted in so many other industries, namely, passing them up a high shaft into the atmosphere. By this means, the inhabitants of the immediate neighbourhood are certainly relieved, but at the expense of those living at a greater distance. The boiled oil is pumped to the top of the building from a tank sunk into the ground at the lowest point of the drain f. Here it is conducted into movable troughs, supported on wheels, which fit into, and run along, the outer part of the iron castings bearing the bars b. The lowest part of the trough is situated immediately above the pieces of scrim, consequently, as soon as the trough is pumped full, the oil begins to overflow at this point. By running the trough backwards and forwards along the length of the shed, the whole of the scrim is uniformly flooded. Although the flooding is sometimes done by hand, yet it is preferable to move the troughs backwards and forwards, by means of chains passing through the end walls of the building, and worked outside by suitable gearing. To prevent the oil from escaping at the side, curtains of canvas, about 6 ft. deep, are hung from the beam h. The sheds are flooded once in 24 hours ; in summer, or when the temperature is high, this operation may be performed twice in the same period. The pumps should be located outside the buildiog, so as to he easily accessible. As the oil soon becomes thick, and full of lumps, ordinary valve-pumps are of little use ; chain-pumps and rotary-pumps have given the best results in practice. To diminish the risk from fire, it is well to isolate each oxidizing shed, and to surround it with a low bank, to prevent the burning oil from spreading, in case of accident. The roof should be covered with iron, although lined with wood, to prevent loss of heat. In calculating the dimensions of the beating apparatus, ample allowance must be made for the diminution of temperature during winter, as any stoppage in the oxidizing department would seriously interfere with the production of the whole manufactory. Each time the scrim is flooded, its surface becomes covered with a thin film of oil, which oxidizes or solidifies, and slightly increases the thickness. In 6-8 weeks, according to the temperature, the total thickness of the cotton fabric and the oxidized oil upon it will amount to about in. ; the whole piece is then known as a " skin." These skins should not be allowed to grow to a greater thickness than in. before removal, as they then become so heavy that they are liable to givo way, causing an interruption in the process. Part of the oil solidifies on the floor of the shed, forming a soft, pasty mass, called " scum." When thick enough, the skins are removed by cutting them immediately below the upper bars, allowing them to fall to the ground, and there cutting them into smaller pieces. The oxidized oil obtained in the above manner, is a yellow, translucent substance, of great elasticity, and possessing a smell somewhat resembling that of fresh paint. It is heavier than water, while the oil from which it was derived is lighter. It is insoluble in alcohol, ether, chloroform, and carbon bisulphide ; even boiling naphtha will only dissolve traces of it. Treated with naphtha, under pressure in a steam-heated pan, it softens without dissolving, and can be worked into a paste in this condition. The only action which dilute acids have upon it is to extract the small quantity of oxide of lead due to the driers. Concentrated sulphuric and nitric acids decompose it rapidly ; hydrochloric acid, slowly. Heated gradually by itself, oxidized oil chars without melting ; it is only when the heat is applied rapidly that the mass becomes partially fused.
The cotton tissue enclosed between the two layers of oxidized oil is found to be completely rotten, the vapours given off by the oil during oxidation having an extremely injurious action, not only upon textile fabrics, but also upon wood, iron, and mortar. Although the quantity of vapour evolved is very considerable, yet the boiled oil gains 11 per cent. in weight when oxidized in the manner described. The bulk of oxygen absorbed must therefore be very large, and indicates the necessity of a plentiful supply of air in the oxidizing buildings. The skins, on coming from the sheds in which they were produced, are ground between ordinary grinding or raising rollers, tho resulting product being then spread out to cool upon a stone or concrete floor, in a layer of 3-4 in. If heaped up in bulk immediately after grinding, the oxidized oil will almost infallibly char,
or ignite spontaneously, when the temperature of the surrounding atmosphere exceeds 21° (70° F.). This dangerous property is probably due to the rapid oxidation of particles of oil which had been enclosed in the skins and are liberated by the process of grinding. The solid nil is, however, capable of still further oxidation ; even long after the linoleum floorcloth has been made and in use, the oil contained iu it continues to harden. It may here be remarked that an asphalte floor soon becomes soft, when exposed to the action of oil.
When freshly ground, the oil feels damp, but it dries in 2-3 hours, and is then ready for the following process. This consists in mixing it with a certain proportion of rosin and kauri gum (son Resinous Substances—Henri, Rosin). The gum, which need not be of the best quality, is first ground under " edge-runners," and sifted ; the rosin is added in lamps. The proportions for ordinary linoleum are :—Oxidized oil, 8i cwt., rosin, 1 cwt., kauri gum, 1 cwt. When linoleum of greater elasticity is required, the following mixture may be used, though it is rather more difficult to work :—Oxidized oil, 8} cwt., rosin, I cwt., kauri gum, tlf cwt. The mixing operation is conducted in a steam-jacketed pan, fitted with an airtight lid or man-hole at the top, and a sliding valve at the bottom, capable of being opened gradually by a screw. Inside the pan, is a shaft carrying stirrers, the whole much resembling a vertical pug-mill, except that the gearing which moves the stirrers must be very massive, on account of the great resistance offered by the oxidized oil, especially at the commencement of each operation. The stirrers having been set in motion, the rosin is first put into the pan, and, as soon as it is melted, the ground oil and kauri are added alternately, in small quantities. When the whole charge is in the pan, the lid is screwed down, and the stirrers are allowed to revolve for a period of 2-4 hours. The steam may be turned off from the steam jacket as soon as the mass has become warm throughout, as the oxidation of the materials suffices to maintain the temperature. A pipe leads the vapours into a furnace, where they are destroyed. Samples are taken from time to time through the lower valve, and, as soon as they appear homogeneous, the valve is opened, and the hot mixture, now termed "cement," is propelled by the action of the stirrers into a pair of cold grinding-rollers immediately beneath. These rollers are hollow, and, in summer, are kept cool by a current of cold water circulating through them. There should be good ventilation in the neighbourhood of the mixing-pan, as the hot cement gives off abundant fumes, which, though not disagreeable when diluted, are extremely pungent in their concentrated state, and have a powerful irritating action on the mucous membranes. After passing through the rollers, the cement is weighed into pans containing 46 lb. each, this being about the quantity required to mix with one sack (56 lb.) of ground cork. The pans are previously whitewashed, to prevent the cement sticking to them. As soon as it has solidified sufficiently, the oement is plaoed on a stone floor to cool, and is then ready for use. Before mixing with the ground cork, the cement is warmed in a room heated to 43°-49° (110°-120° F.). The colour of the cement is much darker than that of the oxidized oil, the amber-yellow of the latter having changed into a mahogany-brown in the mixing pan. The cement is not quite so elastic as the oxidized oil ; but is much tougher, and can be worked into any shape when heated, which is not the case with the oil alone. By varying the proportions of gum and rosin, the degree of hardness and plasticity when heated can be regulated at will. When more generally known, this substance will undoubtedly find many applications in the arts. For instance, its eolution makes an excellent marine glue, which has the advantage of being slightly elastic, and which is, of course, much cheaper than that made with shellac and indiarubber. At present, however, beyond its use for linoleum, it is only applied to making emery wheels. As it can be vulcanized, like indiarubber, it is eminently suited for this purpose, especially as it does not give off such a disagreeable smell when heated as the latter substance dose.