386 SCIENTIFIC RECREATIONS. 



borax (or biborate of soda). Another and inferior quality of this combina- 

 tion is tinkaly found in Thibet. Borax is much used in art and manufac 

 tures, and in glazing porcelain. (Symbol B, Atomic Weight 11). 



SELENIUM is a very rare element. It was found by Berzilius in a 

 sulphuric-acid factory. It is not found in a free state in nature. It closely 

 resembles sulphur in its properties. Its union with hydrogen produces a 

 gas, seleniuretted hydrogen, which is even more offensive than sulphuretted 

 hydrogen. (Symbol Se, Atomic Weight 79). 



TELLURIUM is also a rare substance generally found in combination 

 with gold and silver. It is like bismuth, and is lustrous in appearance. 

 Telluretted hydrogen is horrible as a gas. Tellurium, like selenium, sulphur, 

 and oxygen, combines with two atoms of hydrogen. (Symbol Te, Atomic 

 Weight 129). 



Fig. 393. Casting plate-glass. 



ARSENIC, like tellurium, possesses many attributes of a metal, and on 

 the other hand has some resemblance to phosphorus. Arsenic is sometimes 

 found free, but usually combined with metals, and is reduced from the ores 

 by roasting ; and uniting with oxygen in the air, is known as " white 

 arsenic." The brilliant greens on papers, etc., contain arsenic, and are 

 poisonous on that account. Arsenic and hydrogen unite (as do sulphur and 

 hydrogen, etc.), and produce a foetid gas of a most deadly quality. This 

 element also unites with sulphur. If poured into a glass containing chlorine 

 it will sparkle and scintillate as in the illustration (fig. 395). (Symbol As, 

 Atomic Weight 75). 



Before closing this division, and passing on to a brief review of the 

 METALS, we would call attention to a few facts connected with the metal- 

 loids we have been considering. Some, we have seen, unite with hydrogen 



