IN POPULAR CHEMISTRY. 95 



11. If yon ask for " cobalt" at a drug-store, tvhat will 

 you get? If for "arsenic"? 



Impure metallic arsenic is sold as "cobalt," while arsenious 

 anhydride is called "arsenic." 



12. What two elements are fluid at ordinary tempera- 

 tures ? 



Bromine and mercury. 



13. Should we touch a gold ring to mercury ? 



The mercury will form with the gold an amalgam. 



14. Wliy does silver blacken if handled ? 



The perspiration of the body contains S, which combining 

 with the metal forms silver sulphide, which is black. 



15. IVIiy does silver tarnish rapidly where coal is used 

 for fires ? 



S, which is present in coal, forms a silver sulphide. 



16. Why is a solution of coin blue ? 



From the Cu which is contained in silver coin forming Ou 

 (NO 3 ) 2 , which is blue. 



17. MTIiy will a solution of silver nitrate curdle brine ? 



A white, curdy precipitate of silver chloride is formed. 



18. Wliy does writing with indelible ink turn black 

 when exposed to the sun, or to a hot iron ? 



By the decomposition of the silver salt contained in the 

 ink, and consequent production of Ag 2 O, which stains organic 

 matter black. 



19. What alloys resemble gold ? 



Oroide, aluminum-bronze, etc. 



2O. WJiy does a fish-hook " rust out" the line to which 

 it is fastened ? 



Ferric oxide and ferric hydrate act as conveyers of O, ab- 

 sorbing it from the air and giving it up to organic bodies with 

 which they are in contact. 



