Several hydrated forms of the oxide are known, and a colloidal variety may be obtained by the dialysis of a strong hydrochloric acid solution of sodium molybdate.
Allotropic Modifications.-Sulphur assumes crystalline, amorphous and (possibly) colloidal forms. Historically the most important are the rhombic (Sa) and monoclinic (So) forms, discussed by E.
A colloidal form has been obtained by A.
The colloidal sulphur, Ss, described by Debus as a product of the interaction of sulphuretted hydrogen and sulphur dioxide in aqueous solution, is regarded by Spring (Rec. tra y.
The reactions taking place are complicated, and the solution contains ultimately small drops of sulphur in suspension, a colloidal sulphur (which Spring (Rec. tra y.
Knapp in 1848, and a colloidal modification was described by H.
Schneider and others, have proved the existence of " colloidal silver "; similar forms of the metals gold, copper, and of the platinum metals have been described.
Silica (which is required for the skeletons of diatoms, radiolaria, peridinians, etc.) is present in about the same concentration, but it is now suspected that a source of this substance may be clay washed down from the land and present in the sea in the colloidal form.
The coarser particles of the sediments are deposited near the shore as gravels, sand and muds, but the very fine particles remain in suspension in the colloidal form, and some of this may be acted upon by marine bacteria or (it is surmised) even utilized by diatoms as a source of silica.
The silica, in the form of diatom or radiolarian skeletons, is eventually deposited on the ocean floor after the death of the organisms. Most of the fine colloidal clay is, however, deposited as river-sludges when the fresh water carrying it mixes with denser sea-water.
The colloidal particles are electrically charged and become discharged by the ions of sodium, magnesium and calcium present in the sea-water.
Albumins proper: characterized by having colloidal solutions.
A colloidal or soluble stannic acid is obtained by dialysing a mixture of tin tetrachloride and alkali, or of sodium stannate and hydrochloric acid.
On heating it is converted into colloidal metastannic acid.
A hydrated tin trioxide, Sn03, was obtained by Spring by adding barium dioxide to a solution of stannous chloride and hydrochloric acid; the solution is dialysed, and the colloidal solution is evaporated to form a white mass of 2Sn03 H20.
When freshly prepared it dissolves in cold water to form an indigocoloured solution with a brownish fluorescence of colloidal aurous oxide; it is insoluble in hot water.
Still, according to Murray and Irvine, finely divided colloidal clay is to be found in all parts of the ocean however remote from land, though in very small amount, and there is less in tropical than in cooler waters.
A colloidal variety was obtained by A.
Besides a large number of animal and vegetable substances, many precipitates formed in the course of inorganic chemical reactions are non-crystalline and appear in the colloidal state, instances are the sulphides of antimony and arsenic and the hydroxides of iron and alumina.
The size of the suspended particles in colloidal solutions varies greatly.
Graham obtained a colloidal tungstic acid by dialysing a dilute solution of sodium tungstate and its equivalent of hydrochloric acid; on concentrating in a vacuum a gummy product is obtained, which still remains soluble after heating to 200°, but it is converted into the trioxide on heating to redness.
Many colloidal solutions of copper have been obtained.
Still another view, advocated by Bordet, is that the union of toxin and antitoxin is rather of physical than of strictly chemical nature, and represents an interaction of colloidal substances, a sort of molecular deposition by which the smaller toxin molecule becomes entangled in the larger molecule of antitoxin.
Colloidal silver is the name given by Carey Lea to the precipitates obtained by adding reducing solutions, such as ferrous sulphate, tartrates, citrates, tannin, &c., or to silver solutions.
A colloidal selenium was obtained by C. Paal and C. Koch (Ber., 1905, 38, p. 526) by reducing selenious acid dissolved in an aqueous solution of sodium protalbate with hydrazine hydrate and hydrochloric acid, the precipitate obtained being then dissolved in sodium carbonate.
Microscopic sections show that flint is very finely crystalline and consists of quartz or chalcedonic silica; colloidal or amorphous silica may also be present but cannot form any considerable part of the rock.
It has been suggested that this change is due to the removal of the colloidal silica in solution, leaving behind the fibres and grains of more crystalline structure.
Very finely divided sub-microscopic particles in liquids or in transparent solids can be examined; and the method has proved exceptionally valuable in the investigation of colloidal solutions.
A little clay, stirred up with water in a glass vessel, takes hours to settle, and even after two or three days some remains in suspension; in fact, it has been suggested that in such cases the clay forms a sort of "colloidal solution" in the water.