SENFT ON ROCKS. 





heating in the absence of air, blacken, but which, heated in 

 contact with air, are converted into carbonic acid with evolution 

 of flame, and emitting an empyreumatic, ammoniacal, or bitu- 

 minous odour, therefore volatilizing, and leaving a more or less 

 earthy residue (ash). 



I. Class. SIMPLE CRYSTALLINE BOOKS. 



I. Order. (Hydrolyte.) Rocks soluble in water. 



a. Constituents of water. [1. Group. Ice.~\ 



b. Pure saline taste, but contaminated with oxide of iron, sul- 

 phate of magnesia, or glauber-salt. [2. Group. Bock-salt.'] 



II. Order. (Anhydrolyte.) Rocks insoluble or very little soluble 



in water. 



A. Soluble only in excess of water, particularly when containing 

 common salt or sal-ammoniac. Heated on charcoal, becoming 

 a sulphide. The solution gives the reaction of lime and 

 sulphuric acid. [3. Group. Sulphate of lime. Anhydrite 

 and gypsum.] 



B. Totally insoluble in water, and forming no sulphide on 

 charcoal. 



1 . Soluble in hydrochloric or sulphuric acid, or altered by 



them. 



a. Entirely soluble in acids. 



aa. With evolution of carbonic acid. 



The solution containing lime and also magnesia. [4. 

 Group. Carbonate of lime. Limestone and dolomite.] 



The solution contains protoxide of iron. [5. Group. Car- 

 bonate of iron. Spathose ironstone.] 



bb. Without evolution of gas. 



Protoxide and peroxide of iron ; reddish-brown to black- 

 ish, with red streak ; or metallic grey-black, with bla«kish 

 streak. [6. Group. Iron-ores. Red iron-ore, magnetic 

 iron-ore, sphce.ro siderite, iron-oolite, andpisolitic iron-ore.] 



2. Partially soluble in acids. 

 aa. With deposition of clay. 



Without evolution of carbonic acid. A mechanical mix- 

 ture of clay with oxide of iron, of ochre-yellow or brown 

 colour. [Iron-ores, as B. 1, bb.] 



With evolution of carbonic acid (see Group 4). Marl. 



bb. With deposition of gelatinous silica. Dark-coloured, 

 grey to blackish-green, and greyish-black, soft rocks, 

 dense or slaty, greasy or meagre. [7. Group. Magnesia. 

 (In part argilloid.) Clay-slate, slaty clay, chloritic 

 slate, and serpentine.] 



