Tellurium solution, colloidal

Colloidal Tellurium.—On reduction of dilute solutions of tellurium dioxide or telluric acid by means of hydrazine, hydroxylamine, hypo-phosphorous acid, sulphurous acid or salts of these compounds, brown or blue colloidal solutions can be obtained, the stability of which is greatly increased by the presence of an organic colloid such as gum arabic, sodium lysalbate or sodium protalbate.8 Similarly the addition of an extract of the seeds of Plantago psyllium, in amount not exceeding 0-3 per cent., renders extremely stable the sols obtained by the reduction of telluric acid with hydrazine hydrate.9 Stable sols may also be obtained by the reduction of telluric acid with dextrose in the presence of ammonia. Dialysis does not completely remove the adsorbed dextrose and this undoubtedly contributes to the remarkable stability.10 The particles of colloidal tellurium in these sols are negatively charged. 

Various other methods of preparing colloidal tellurium have been described. If a small quantity of the element is dissolved in a boiling solution of potassium hydroxide and the product poured into a large bulk of cold water with vigorous stirring, tellurium remains in colloidal solution.12 Colloidal aqueous solutions have also been produced by... 

Water is without effect on the element even at a red heat,3 but the combined action of water and ozone produces telluric acid at the ordinary temperature.4 The action of hydrogen peroxide upon tellurium is influenced considerably by the physical state of the element colloidal tellurium is readily oxidised, but crystalline tellurium is not readily attacked and has first to be dissolved in an aqueous solution of alkali hydroxide, when oxidation becomes possible with formation of tellurate.5 Hydrogen peroxide of 60 per cent, strength reacts very slowly with tellurium at a temperature of 100° C., but with increasing amount of telluric acid formed, the rate of dissolution increases. Amorphous tellurium as ordinarily prepared behaves in a similar manner to the crystalline variety, but if it is dried by treatment with alcohol and ether instead of by heating at 105° C. it will dissolve readily in a concentrated solution of hydrogen peroxide.6... 

An aqueous solution of telluric acid gives with hypophosphorous acid a colloidal solution of tellurium which is precipitated completely on boiling and can then be filtered and weighed. This method is only available if there are no other salts present which might be reduced.6... 

Metallic potassium and sodium are explosively converted into the hydroxides when brought into contact with concentrated solutions of hydrogen peroxide many of the heavier metals such as zinc and iron, and especially aluminium,3 are readily changed into their respective hydroxides, whilst chromium, arsenic, and molybdenum are oxidised respectively to chromic, arsenic, and molybdic acids. Colloidal tellurium yields telluric acid with very dilute solutions of peroxide4 the crystalline modification reacts slowly with 60 per cent, peroxide at 100° C. 

---