514 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



ounce weight falls upon it from an elevation of twelve feet, 

 it receives not the slightest impression. 12 A, XI., 474. 



AKTIFICIAL GEMS OF HARDENED GLASS. 



Mackintosh has patented a j^rocess for hardening glass, 

 mainly for the manufacture of very hard artificial gems, by 

 which he hopes to produce these superior to the diamond in 

 hardness, and to furnish a glass powder superior to diamond 

 dust and emery for grinding purposes. The process differs 

 from that recently introduced for hardening glass, as the 

 glass is cooled in platinum moulds, in a freezing mixture. 

 8 (7, XII., 1875, 311. 



WATER-GLASS FOR WASHING COTTON USED IN CLEANING 



MACHINERY. 



According to the Hessische Geicerbe-Blatt, cotton that has 

 been used for cleaning machinery may not only be complete- 

 ly cleansed by treatment with water-glass without affecting 

 the fibre or color, but it is also rendered softer and more 

 porous, and consequently preferable to new material, since it 

 takes up oily matter more readily. 6 (7, 1875, 29. 



TINNING IRON TACKS. 



According to Wiley, the process is to triturate chloride of 

 zinc with a large quantity of oil, and heat it in an oscillating 

 vessel, and, as soon as it has reached the proper temperature, 

 throw in the tacks and the necessary quantity of metallic 

 tin, and after a few seconds dip them out with wire gauze, 

 and cast them into water. 5 (7, XL., 104. 



BRILLIANT ZINC COATING ON BRASS AND COPPER. 



The following simple process is recommended by Bottger: 

 Boil a large excess of so-called zinc dust some time with a 

 concentrated solution of caustic soda, or potash, and place 

 the copper or brass articles to be coated in the boiling liquid. 

 By continuing the heating, after a few minutes a beautiful, 

 mirror-like film of zinc will form upon them, by the decom- 

 position of the alkaline solution, in consequence of their elec- 

 tro-necrative character in combination with the zinc. It is 

 suggested that the process is applicable to the preparation 

 of disks for dry-piles, and also for forming a layer of tombac, 



