PHILOSOPHICAIi SOCIETY OP WASHINGTON. 79 



III, Nonmetallic injlammable subslances— 



Sulphur, Diamond, Coal, &c. 



IV. Metallic substances — 



Gold, Silver, &c! 



Werner also distinguishes four classes : 



I. Earthy substances — 



Diamond, Augite, Garnet, &c. 



II. Saline substances — 



Soda, Saltpetre, &c. 



III. Injiavimahle substances — 



Coal, Graphite, &c. 



IV. Metallic substances — 



Gold, Silver, Arsenic, &c. 



Between these two systems there is practically very little differ- 

 ence, and that of Weiss resembles them greatly in its main out- 

 lines. He decides upon seven orders : 

 I. Oxydic rocks, or Silicates j 



II. Saline rocks; 



III. Saline ores; 



IV. Native metals; 

 V. Oxydic ores; 



VI. Siilphurets and sulphides of metals; 

 Vll. Injlammabilia ; 



More arbitrary, however, is the system of Mohs, accepting three 

 classes : 



I. Gases, water, acids, salts (Soda, Nitre, &c. ). 

 II. Haloids (Gypsum, Fluorite, &c. &c.). 

 Ill Gums and coal. 



The chemical system as proposed by Berzelius contained two 

 groups with four orders : 



A. Oxygen. 



I. Oxygen. 



B. Inflammable substances. 



I. Metalloids, 

 II. Electro-negative metals, 



III. Electro-positive metals, closing with Sulphates, Ni- 

 trates, and Silicates. 



He modified this system, however, and proposed a classification 

 having two orders: 



A. Non-oxidized substances. 



B. Oxidized substances, arranged according to the electro- 



negative substance. 



With Dana's system everyone is familiar, so that need not 

 further be enumerated here. 



In a chemical system we have at hand the means by which a 



