D. CHEMISTRY AND METALLURGY. 61 



water. It is then immersed in a silver bath until the entire 

 surface of the relief is moistened. A copper wire, bent at 

 right angles, is now to be moved over the horizontal surface 

 of the object so as to touch the surface when placed in the 

 sunlight. The silver is then deposited in the form .of little 

 rays upon the copper wire, and becomes a lustrous continuous 

 coating upon that portion of the object touched by the cop- 

 per. The plate is next to be taken out as horizontally as pos- 

 sible from the solution, and laid in the sunlight to dry. The 

 superfluous silver is then to be washed off with water, leaving 

 behind a silvery layer, which is an excellent conductor of the 

 galvanic current, so that a satisfactory result will be obtained 

 with a small amount of electricity. 14 (7, C, 315. 



GILDIXG AND SILVERING SILK. 



According to a formula published by Grtine for silvering 

 or gilding silk, the silk is to be soaked with a five per cent, 

 solution of iodide of potassium, and dried; then (in non-ac- 

 tinic light) dipped in a five per cent, solution of nitrate of 

 silver, containing a few drops of nitric acid, and well drain- 

 ed; next exposed for a few minutes to sunlight, and then 

 dipped in a two per cent, solution of sulphate of iron. It 

 immediately becomes gray from reduction of metallic silver, 

 and, after washing and drying, only requires burnishing in 

 order to acquire the metallic lustre. By repeating this treat- 

 ment, varied, however, by adding a little free iodine to the 

 solution of iodide of potassium, the silver deposit becomes 

 stronger. By laying the silvered silk in a very weak solution 

 of chloride of gold the silver becomes chloride, and gold is 

 deposited ; and by then removing the chloride of silver by a 

 solution of hyposulphite of soda, lvashing, drying, and bur- 

 nishing, the appearance of gilding is produced, if the deposit 

 of metal be sufficiently thick. The purest chemicals must 

 be used in order to secure satisfactory results. Jour. Chem. 

 /Soc. Lonely 1871, Jime, 450. 



MICROSCOPIC CHARACTER OF IRON AXD STEEL. 



According to Mr. Schott, the different qualities of iron and 

 steel can readily be distinguished by means of the micro- 

 scope. Thus the crystals of iron are double pyramids, in 

 which the proportion of the axes to the bases varies with the 



