MANUAL OF NATURAL HISTORY, 615 



bases. Titanic acid if fused with an alkali 

 is soluble in dilute hydrochloric acid, in 

 which a solution of gall-nuts causes an orange 

 red colour. Symb. Ti. 

 8. Family. — Tungstenides. Minerals containing 

 principally compounds of Tungsten. Oc- 

 cur 1, as Oxide or "Tungstic acid/' with 

 iron and manganese as " Wolfram/' trimetric, 

 H. = 5, sp. gr. = 7*3, dark brown ; 2, with 

 calcia (lime) as " Scheelite/' in square octa- 

 hedrons, H. = 4*5, sp. gr. = 6, white. Wolfram 

 readily fuses before the blowpipe into a mag- 

 netic globule studded with crystalline points. 

 Symb. W. 

 9. Family. — Molybdenides. Minerals principally 

 composed of compounds of Molybdenum. 

 Occur 1 , as Oxide or " Molybdic-ochre/' an 

 earthy yellow powder, yielding a yellow glass 

 with Microcosmic salt ; 2, as Molybdic-acid 

 with lead or "Wulfenite/' in square octo- 

 hedrons, or very short prisms, H. == 2*8, sp. 

 gr. = 6*5, yellow; 3, as bisulphuret or 

 " Molybdena/' hexagonal, H. = 1—1*5, sp. 

 gr. = 4*5, feel unctuous, lustre metallic, 

 lead-gray. Symb. Mo. 



VI. ORDER— Iridexides. 



Minerals containing metals of the Iridium series. 

 1. Family. — Iridiides. Minerals containing Iri- 

 dium. Occur 1, alloyed with Osmium as 

 « Iridosmine," H. = 6 -7, sp. gr. = 19-21, 



