It is the viscous or graisse disease.
Free from bubbles, it is allowed to cool down to a certain extent so as to become viscous or pasty.
The solid melts to a pale yellow liquid which on continued heating gradually darkens and becomes more viscous, the maximum viscosity occurring at 180°, the product being dark red in colour.
Liquid selenium becomes more and more viscous in character as its temperature falls from 220° C. to 60° C.; it is soft at about 60°, but is hard and brittle between 30° and 40°.
Some of the more viscous crude oils obtained in the United States are employed as lubricants under the name of " natural oils," either without any treatment or after clarification by subsidence and filtration through animal charcoal.
The ice-cap of Greenland must to some extent be considered as a viscous mass, which, by the vertical pressure in its interior, is pressed outwards and slowly flows towards the coasts, just as a mass of pitch placed on a table and left to itself will in the course of time flow outwards towards all sides.
At higher temperatures the viscous liquid suffers decomposition with the formation of various liquid hydrocarbons, principally members of the terpene series.
In the viscous state a mass of glass can be coiled upon the heated end of an iron rod, and if the rod is hollow can be blown into a hollow bulb.
A flattened cake of viscous glass-enamel is welded on to one side of the mass of glass after it has been hollowed by blowing.
The pressure causes the soft metal to flow like a viscous solid, but its lateral escape is prevented by a collar which surrounds the blank while it is being struck.
As the larva approaches maturity these vessels become gorged with a clear viscous fluid, which, upon being exposed to the air immediately hardens to a solid mass.
But immediately above this level the charge is relatively viscous, because here the temperature has fallen so far that it is now at the melting or formation point of the slag, which therefore is pasty, liable to weld the whole mass together es so much tar would, and thus to obstruct the descent of the charge, or in short to " scaffold."
A cold lump of ore chills the slag immediately around it, just where its oxygen, reacting on the carbon of the metal, generates carbonic oxide; the slag becomes cool, viscous, and hence easily made to froth, just where the froth-causing gas is evolved.
Yet frothing is not excessive, because the slag is not, as in common practice, locally chilled and made viscous by cold lumps of ore.
The tools used are extremely primitive - hollow iron blowing-rods, solid rods for holding vessels during manipulation, spring tools, resembling sugar-tongs in shape, with steel or wooden blades for fashioning the viscous glass, callipers, measure-sticks, and a variety of moulds of wood, carbon, cast iron, gun-metal and plaster of Paris (figs.
The basic lavas are usually darker and denser than lavas of acid type, and when fused they tend to flow to great distances, and may thus form far-spreading sheets, whilst the acid lavas, being more viscous, rapidly consolidate after extrusion.
Certain nerve fibres from the sympathetic nervous system, which can also cause the secretion of a (specially viscous) saliva, are entirely unaffected by atropine.
Again, it is well known that in the case of the viscous disease the difficulty may be overcome by the addition of a small quantity of tannin.
Asphalt, whether a natural product or artificially obtained, as, for example, in some chemical manufactures, is a most useful material if properly employed in connexion with reservoir dams. Under sudden impact it is brittle, and has a conchoidal fracture like glass; but under continued pressure it has the properties of a viscous fluid.
But given time, all such compounds, if they contain enough bitumen to render them water-tight, appear to settle down even at ordinary temperatures as heavy viscous fluids, retaining their fluidity permanently if not exposed to the air.
The smooth surface of the viscous billowy lava is further diversified by long twisted " ropes," curving backwards and forwards up and down the undulations.
The opening of the mouth is small, and from it the echidna puts forth its long slender tongue, lubricated with a viscous secretion, by means of which it seizes the ants and other insects on which it feeds.
If the viscous variety be rapidly cooled, or the more highly heated mass be poured into water, an elastic substance is obtained, termed plastic sulphur.
Persulphuric anhydride, S207, is a thick viscous liquid obtained by the action of the silent discharge upon a mixture of sulphur trioxide and oxygen.
In his eighteenth year, while still a student in Edinburgh, he contributed two valuable papers to the Transactions of the same society - one of which, " On the Equilibrium of Elastic Solids," is remarkable, not only on account of its intrinsic power and the youth of its author, but also because in it he laid the foundation of one of the most singular discoveries of his later life, the temporary double refraction produced in viscous liquids by shearing stress.
The more viscous descriptions of mineral oils have also been found suitable for use in the Elmore process of ore-concentration by oil.
As the rock was highly viscous and the surface over which it moved was often irregular the motion was disturbed and fluctuating; hence the sinuous and contorted appearance frequently assumed by the banding.
These crystallites (q.v.) show that the glassy rock has a tendency to crystallize which is inhibited only by the very viscous state of the glass and the rapidity with which it was cooled.
There must, then, be a relation between the rate of change of the concentration and the osmotic pressure gradient, and thus we may consider the osmotic pressure gradient as a force driving the solute through a viscous medium.
At about 150 0 -200° C. caoutchouc melts, forming a viscous liquid which does not solidify on cooling.
This viscous liquid is present in small proportion in some commercial rubbers owing to overheating during their preparation.
They pass through a viscous stage in cooling from a state of fluidity; they develop effects of colour when the glass mixtures are fused with certain metallic oxides; they are, when cold, bad conductors both of electricity and heat, they are easily fractured by a blow or shock and show a conchoidal fracture; they are but slightly affected by ordinary solvents, but are readily attacked by hydrofluoric acid.
A mass of glass in a viscous state can be rolled with an iron roller like dough; can be rendered hollow by the pressure of the human breath or by compressed air; can be forced by air pressure, or by a mechanically driven plunger, to take the shape and impression of a mould; and can be almost indefinitely extended as solid rod or as hollow tube.
So extensible is viscous glass that it can be drawn out into a filament sufficiently fine and elastic to be woven into a fabric.
The stirring process is begun when the glass is perfectly fluid at a temperature little short of the highest attained in its fusion, but as the stirring proceeds the glass is allowed to cool gradually and thus becomes more and more viscous until finally the stirring cylinder can scarcely be moved.
It is a curious property of viscous glass that whatever form is given to the mass of glass before it is drawn out is retained by the finished cane or tube, however small its section may be.
When this is the case the gathering is carried to a block or half-open mould in which it is rolled and blown until it acquires, roughly, the shape of a hemisphere, the flat side being towards the pipe and the convexity away from it; the diameter of this hemisphere is so regulated as to be approximately that of the cylinder which is next to be formed of the viscous mass.
The whole pot, with its contents of viscous glass, is then removed bodily from the furnace by means of huge tongs and is transported to a crane, which grips the pot, raises it, and ultimately tips it over so as to pour the glass upon the slab of the rolling-table.
The viscous mass having been thrown on the casting-table, a large and heavy roller passes over it and spreads it out into a sheet.
As liquidity might be looked upon as the ne plus ultra of softness, this is the right place for stating that, while most metals, when heated up to their melting points, pass pretty abruptly from the solid to the liquid state, platinum and iron first assume, and throughout a long range of temperatures retain, a condition of viscous semi-solidity which enables two pieces of them to be "welded" together by pressure into one continuous mass.
Every solid substance is found to be plastic more or less, as exemplified by punching, shearing and cutting; but the plastic solid is distinguished from the viscous fluid in that a plastic solid requires a certain magnitude of stress to be exceeded to make it flow, whereas the viscous liquid will yield to the slightest stress, but requires a certain length of time for the effect to be appreciable.
But when the smallest stress, if only continued long enough, will cause a perceptible and increasing change of form, the substance must be regarded as a viscous fluid, however hard it may be."
In considering the motion of a fluid we shall suppose it non-viscous, so that whatever the state of motion the stress across any section is normal, and the principle of the normality and thence of the equality of fluid pressure can be employed, as in hydrostatics.
His observations led him to the view that a glacier is an imperfect fluid or a viscous body which is urged down slopes of a certain inclination by the mutual pressure of its parts, and involved him in some controversy with Tyndall and others both as to priority and to scientific principle.
It is almost colourless and has a small coefficient of expansion; its hygroscopic properties, its viscous character, and its action on the skin, however, militate against its use.
There is no " transverse " disturbance, that is, there is in air no motion across the line of propagation, for such motion could only be propagated from one layer to the next by the " viscous " resistance to relative motion, and would die away at a very short distance from the source.
That of helping the thin viscous threads through their final outlets, and the adhesion of the two filaments when brought into contact with the atmosphere.
But while Forbes asserted that ice was viscous, Tyndall denied it, and insisted, as the result of his observations, on the flow being due to fracture and regelation.
All agreed that ice flowed as if it were a viscous fluid; and of this apparent viscosity James Thomson offered an independent explanation by the application of pure thermodynamical theory, which Tyndall considered inefficient to account for the facts he observed.
As far as the order to which he carried the approximations - which, however, were based on a simplifying hypothesis that the molecules influenced each other through mutual repulsions inversely as the fifth power of their distance apart--the result was that the equations of motion of the gas, considered as subject to viscous and thermal stresses, could be satisfied by a state of equilibrium under a modified internal pressure equal in all directions.
Old trees are selected, from the bark of which it is observed to ooze in the early summer; holes are bored in the trunk, somewhat inclined upward towards the centre of the stem, in which, between the layers of wood, the turpentine is said to collect in small lacunae; wooden gutters placed in these holes convey the viscous fluid into little wooden pails hung on the end of each gutter; the secretion flows slowly all through the summer months, and a tree in proper condition yields from 6 to 8 Ib a year, and will continue to give an annual supply for thirty or forty years, being, however, rendered quite useless for timber by subjection to this process.