CHEMISTRY. 269 



Ibs. equal to 88*5 Ibs. in favor of the castings produced from the improved 

 coke, or in the ratio of 5 to 4. 



The experiments on the bars smelted with the unproved coke, indicated 

 iron of a high order as to strength, and might be considered equal to the 

 strongest cold blast iron. The metal appeared to have a run exceedingly 

 close, and exhibited a compact granulated structure, with a light grey color. 



IMPROVEMENTS IN PLATING, GILDING, AND SILVERING. 



Liebig's Process. The following are the details of a process recently 

 published by Liebig, by means of which glass can be plated without heat, 

 thus forming faultless optical mirrors. The bath which gives the desired 

 result is a solution of ammoniacal nitrate of silver, with the addition of 

 potassa or soda, which deposits the silver at the ordinary temperature when 

 put in contact with an aqueous solution of sugar of milk La the following 

 proportions : Fused nitrate of silver, 10 grs. ; distilled water, 200 c.c. ; 

 ammonia, sufficient to obtain a limpid solution ; to which is added by degrees 

 potash ley of 1'05 density 450 c.c., or soda ley of 1'035 density 450 c.c. 

 When the ley is added, a dark-colored precipitate is formed, which disappears 

 on the addition of a further quantity of ammonia. When all the ley has been 

 added, it is diluted with water to 1450 c.c., after which a dilute solution of 

 nitrate "of silver is carefully added until a permanent grey precipitate is 

 produced. Sufficient water is then added to bring the quantity up to 1500 

 c.c., or a litre and a half of liquid, so that each cubic centimetre contains 

 rather more than 6 '66 milligrammes of nitrate of silver, corresponding to 4*18 

 milligrammes of metallic silver. The liquid should not contain any free 

 ammonia ; this alkali should be completely saturated by the oxide of silver. 

 To get a complete saturation, a little of the silver solution should be added 

 quite at last. In this case, 1 c.c. of liquid contains rather less than 4'18 milli- 

 grammes of silver in solution. The potassa or soda ley should be quite free 

 from chlorides ; to prepare it, carbonate of potassa, or preferably, of soda, 

 should be used, quite free from chlorides, and decomposed in distilled water 

 with lime which has been purified by sufficient washing. The ley must not 

 be filtered, it must become clear by repose. When this ley is required for 

 plating glass, add one-tenth or one-eighth of its volume of a solution of sugar 

 of milk, containing 10 per cent, of sugar. To use these liquids, the glass must 

 be supported by fastening a bar of tin at the back of the glass with wax, so 

 that it can be suspended ; under which is placed a glass or porcelain capsule, 

 so that a space of half an inch is left between the bottom of the capsule and 

 the surface to be silvered; the capsule is then filled with the liquid, to which 

 the sugar of milk has just been added, and the whole is arranged so that the 

 object to be silvered shah 1 have its anterior surface quite immersed. It will 

 be perceived that the silvering should take place at the surface of the bath, 

 and not at the bottom, and that it is indispensable that the glass object should 

 float and be supported in some manner upon the surface. It is necessary not 

 to mix the sugar of milk with the bath until the moment of using, for the 

 reduction commences immediately, as will be known by the brown color 

 which it acquires; the object immersed becomes black in a few minutes; 



