410 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



pounds, and complete crushing only with a pressure of 1000 

 pounds, while some blocks resisted a pressure of 1300 or 1400 

 pounds. 18 C, xix., May 10,303. 



CEMENT FROM FURNACE SLAG. 



Furnace slag can be made to furnish an excellent cement 

 by selecting such portions of it as are readily dissolved in 

 dilute hydrochloric acid. On subjecting it to the action of 

 the acid silica is thrown down, which is afterward to be 

 washed, dried, and pulverized. One part of this is next to 

 be mixed with nine parts of powdered slag and the necessary 

 quantity of slacked lime. This matter soon hardens, and ri- 

 vals the best cement in its durability. 9 C, January, 1871, 3. 



BLACKENING STONE. 



A method of rendering stone completely black, to serve as 

 a foil to some other color, or to protect it against the weath- 

 er, consists in heating it in an oven to about 140, and then 

 removing it and dipping the side to be colored into a vessel 

 filled with melted tar. After removal the surplus is allowed 

 to drain off, and laid not far from the stove to dry. When 

 it is half dried, it is placed in the air and allowed to become 

 completely dry, after which a wisp of straw is used to rub off 

 the blackened side, which gives to the stone a brilliant lustre, 

 and prepares it for farther use. 9 (7, March, 1870, 17. 



PROTECTION OF STONE BY SALTS OF COPPER. 



Dr. Robert, of Paris, recommends earnestly the use of salts 

 of copper as the best j^reservative against the weathering of 

 stone in a moist climate, and endeavors to prove that the 

 wasting away of sandstone and granite is due to various 

 causes, one of the most important of which is the develop- 

 ment of a minute lichen (the Lepra antiquitatis). This plant 

 is so destructive that the beautiful marble sculptures in the 

 park at Versailles would be completely destroyed by it in 

 the space of fifty years unless precautions were taken to ar- 

 rest its ravages. Dr. Robert states that the amount of weath- 

 ering away of rocks of all kinds, granite not excepted, is much 

 greater than the public generally are aware of, especially 

 when subjected to the influence of a moist atmosphere. Thus 

 the obelisk of Luxor, which was brought to Paris from Egypt 



