D. CHEMISTRY AND METALLURGY. fl 



gested as the result of the chemical relationship dwelt upon. 

 Thus many of the practical applications of this substance 

 depend especially upon the separation of silicic acid, and are 

 more efficient in proportion to the amount and completeness 

 of this separation. If, therefore, surfaces which are to be 

 silicified are coated alternately with water-glass and a solu- 

 tion of common salt, they will ultimately be found to possess 

 a harder and more uniform exterior. By first saturating 

 stone or wood with a solution of sal ammoniac, or common 

 salt, and adding the water-glass before the former application 

 is completely dry, the result will be found to be very satis- 

 factory. 2 C\JVov., 1870, 105. 



IODINE FKOM CHILE SALTPETRE. 



Iodine is said to be now manufactured on a large scale 

 from Chile saltpetre (nitrate of soda), over thirty thousand 

 pounds per annum being obtained. The process consists in 

 treating the liquids resulting from the manufacture of salt- 

 petre with a mixture of sulphurous acid and sulphite of soda, 

 in proper proportion, when the iodine falls to the bottom as 

 a black precipitate. This is allowed to drain on layers of 

 quartz sand, and is then removed, and finally purified by sub- 

 limation. Panama Star and Herald, Jan. 1 7. 



RESTORING SPENT SULPHURIC ACID. 



A patent has lately been taken out in England for restor- 

 ing spent sulphuric acid, and the inventor of the process 

 claims that by its means he can revivify the acid so cheaply 

 that the same weight can be obtained for one cent that now 

 costs seven in new acid. The method consists essentially in 

 heating the spent acid in a vessel of peculiar construction 

 with dry steam to a temperature of about 120, after which 

 six or seven pounds of black oxide of manganese are to be 

 sprinkled into it, and more steam is turned on. The tank is 

 then covered, and care must be taken to prevent its foaming 

 over ; should any thing of this kind be threatened, the steam 

 must be turned off for a short time, and the foam will sub- 

 side. The heating is kept up six or eight hours, and then the 

 liquid allowed to cool, after which any oil or tar that has 

 come to the surface is to be skimmed off, leaving the restored 

 acid behind. 8 A, Jan., 1871, 12. 



