466 OXIDISED OIL 



which neutralise basic oxides, combining with them ; and neutral oxides, -which do 

 not unite with either bases or acids. In addition to these, are saline oxides, or com- 

 pounds which are produced by the union of two oxides of the same metal. 



OXIDHS, for polishing. The finest croons and jeweller's rouge are thus prepared : 

 Crystals of suiphate of iron are taken from the pans in which they have crystallised, 

 and are put at once into crucibles, or cast-iron pots, and exposed to a high tempera- 

 ture ; the greatest care being taken to avoid the presence of dust. 



The least-calcined portions are of a scarlet colour, and form the jewellers' rouge for 

 polishing gold or silver articles. The more calcined portions are of a purple or 

 bluish-purple colour, and these form crocus for polishing brass or steel. It is found 

 that the blue particles, which are those which have been exposed to the greatest heat, 

 are the hardest. It will, of course, be understood that the result of the action of heat 

 is to drive off the sulphuric acid from the protoxide of iron, which becomes peroxidised 

 in the process. 



Lord Eosse, in the 'Philosophical Transactions,' thus describes his process of pre- 

 paring his polishing powder : 



' I prepare the peroxide of iron by precipitation with water of ammonia, from a 

 pure dilute solution of sulphate of iron. The precipitate is washed, pressed in a 

 screw-press till nearly dry, and exposed to a heat, which in the dark appears a dull 

 low red. The only points of importance are, that the sulphate of iron should be 

 pure, and the water of ammonia should be decidedly in excess, and that the heat 

 should not exceed that I have described. The colour will be a bright crimson, 

 inclining to yellow. I have tried both potash and soda pure, instead of water of 

 ammonia, but after washing with some degree of care, a trace of the alkali still re- 

 mained, and the peroxide was of an ochrey colour, and did not polish properly.' 



Jewellers' rouge is, however, frequently prepared in London by precipitating 

 sulphate of iron with potash, well working the yellow oxide, and calcining it until it 

 acquires a scarlet colour. 



Crocus is sometimes prepared after the manner recommended by Mr. Heath. 

 Chloride of sodium and sulphate of iron are well mixed in a mortar; the mixture is 

 then put into a shallow crucible, and exposed to a red heat. Vapour escapes and the 

 mass fuses. "When no more vapour escapes, remove the crucible, and let it cool. 

 The colour of the oxide of iron produced, if the fire has been properly regulated, is u 

 fine violet if the heat has been too high it becomes black. The mass when cold is 

 to be powdered and washed, to separate the sulphate of soda. The powder of crocus 

 is then to be submitted to a process of careful elutriation, and the finer particles 

 reserved for the more delicate work. 



OXIDES OP IRON. Four definite combinations of iron and oxygen are known, 

 namely: Protoxide, FeO; sesguioxide, Fe 2 0* ; black or magnetic oxide, Fe*0 4 = 

 FeO, Fe 2 s ; Ferric acid, FeO 3 . See IKON. 



OXIDES OP XiEAD and TIN. These are both used for polishing. For oxide 

 of tin, see PCTTY POWDER. 



OXIDISED Oil.. At a meeting of the Society of Arts, on April 4, 1862, Mr. 

 Frederick Walton read a paper ' 'On the introduction and use of elastic gums and 

 analogous substances,' which described a new preparation bearing the above name. 

 The following is Mr. Walton's description of the manufacture : 



' Whilst engaged, about two years ago, in a series of experiments on the manu- 

 facture of artificial leather, it was of the greatest importance to the success of the 

 material that it should have a coat of fine varnish, which, whilst drying quickly, 

 possessed the flexibility of india-rubber. Copal varnish has always been accounted 

 the best varnish, but made with drying oil combined with gum opal at a high tem- 

 perature, it will not, of course, be dry, until the action of oxidation has reduced the 

 oil contained therein into a solid film. Whilst revolving in my mind this knotty 

 difficulty, and presenting every phase of it to careful thought, it suddenly occurred to 

 me that if the oil was first dried into a skin, like those I had often seen on paint-cans, 

 but, like other people, had before considered as waste, was dissolved in a volatile 

 solvent, like india-rubber sheet, that the semi-resinous material would immediately, 

 on the evaporation of the solvent, resume, like india-rubber, the form it was in prior 

 to solution. By dipping panes of glass into linseed oil, and allowing the films or 

 layers to dry, then repeating the process, I imitated the manufacture of india-rubber 

 from the milk, and thereby produced a solid elastic substance, composed of many 

 layers of perfectly oxidised oil. Up to this stage I had done nothing new or original, 

 for the oil-sheet manufacturers have for more than a century waterproofed linen by 

 layers of oil. But to treat this semi-resinous matter and render it available to pur- 

 poses of manufacture, will be admitted to be perfectly new, and I now proceed to 

 describe the invention. Having accumulated a quantity of solid oxidised oil by dry-ing 

 it upon extensive surfaces of any kind, such as prepared cloth, stretched in frames, as 



