1 8 73-1 Technology. 143 



out upon a smooth surface, such as glass, the latter having first been moistened 

 to aid the laying out of the tin, and to maintain it in its position. The 

 painting, when dried and varnished, can be rolled up like ordinary paper- 

 hangings, from which it essentially differs in possessing all the variety of tones 

 and colouring that oil paintings admit of. The tin groundwork constitutes a 

 water-proof protection, and, on account of its great flexibility, will follow the 

 various mouldings and contour of the object to be ornamented. To the latter 

 should be applied a hydrofuge mixture; it will then be ready for the decorator. 

 Ordinary gilding may be replaced by this method, as the gold can be applied 

 in the workmanship and the gilt tin fixed afterwards. The advantage of gilt 

 tin over gilding on other, metals is, that it is inimical to oxidation ; whereas it 

 is known that gilding upon other metals, and notably upon zinc, deteriorates 

 rapidly. 



A quantity of tin in ingots was, during a severe frost, sent from Rotterdam 

 to Moscow. On arriving it was found to be in a coarse crystalline powder, 

 which could not be fused into the ordinary condition of tin ; for, on the appli- 

 cation of heat, it was almost entirely converted into oxide of tin, the appear- 

 ance of which closely resembled sulphide of molybdenum. On being analysed 

 it was found to contain 997 per cent of pure tin, the remainder being lead 

 and iron. The cause of the change was attributed to the long-continued 

 vibration it underwent at so low a temperature. Similar conditions have 

 been known to render wrought-iron extremely brittle, and its texture crystalline 

 and granular. 



M. Marion, of Paris, has devised a method of photographic printing; it 

 consists in impregnating paper with ferroprussiate, which renders it sensitive 

 to light. The drawing, which is made on tracing paper, is laid upon the sen- 

 sitive paper as a negative and exposed to light, after which the sensitive paper 

 is washed in water ; the copy is then found to be produced on it in white 

 line on a blue ground, which may be changed to black, the drawing still 

 remaining white by using a tannin solution. 



The French Mint has recently coined, for the Bank of France, 6000 or 

 7000 lbs. of Australian Gold, known as " brittle." All the pieces have been 

 found to be easily broken, and have, therefore, to be re-melted. The defect 

 is attributed to the presence of a small percentage of antimony and arsenic, 

 extremely difficult of removal. These elements are known to produce a 

 similar effect in all metals or alloys that are subject to the molecular changes 

 induced by the pressure and heat developed under the action of the dies in 

 the coining press. 



Owing to the fact that water-glass is gradually dissolved out of wood while 

 chloride of zinc is volatile at the temperature at which wood ignites, Dr. 

 Sieburger proposes as a fire-proof paint for woodwork the following : — Two 

 coats of a hot saturated solution of 3 parts alum and 1 part ferrous sulphate 

 are first applied and allowed to dry. The third coat is a dilute solution of 

 ferrous sulphate, into which white potter's clay is stirred until it has the con- 

 sistency of good water-colours. Another method is to apply hot glue-water 

 as long as it is absorbed into the pores of the wood. A thick coat of boiled 

 glue is then applied, and while fresh is dusted over with a powder composed 

 of 1 part sulphur, 1 part ochre or clay, and 6 parts of ferrous sulphate. 



M. Tatro, the inventor of a process for purifying petroleum, states that by 

 adding from 2 to 4 per cent of sulphuric acid, and 4 to 6 per cent of dry lime, 

 agitating the oil with this mixture, and proceeding with the distillation, a 

 larger proportion of burning oil is produced. 



Palmetto leaves have recently been shipped from Savannah to England for 

 the purpose of testing their value in the manufacture of paper. 



CHEMICAL SCIENCE. 



Having ascertained that furfurol is formed when wood is heated with water 

 to an elevated temperature and pressure, Mr. Greville Williams, F.R.S, ex- 

 plains the method by which he found it to be produced by the action of high- 



