P-ROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 709 



Pounds 

 Avoirdupois. 



Galena, the common sulphuret of lead, used to produce pig lead, 



etc., has a specific gravity of Y.5, and a cubic foot weighs .... 465 

 Gold, specific gravity (tM'^enty carats) 15.7, up to (pure) 19.2, 



and the average M^eight of a cubic foot 1,000 to 1,200 



Gypsum, or plaster of Paris, has a specific gravity of 2,3, and a 



cubic foot weighs 130 



Iron — cast iron, a cubic foot weighs 450 



Magnetic ore has a specific gravity of 5>.0, and a cubic foot 

 weighs 310 



Spathic ore has a specific gravity of 3.0, and a cubic foot 

 weighs .' 200 



Pyrites, or bisulphide of iron, has a specific gravity of 5.0, and 

 a cubic foot weighs 310 



Pyrrliotine, or magnetic pyrites, or sulphuret, has a specific 

 gravity of 4.5, and a cubic foot weiglis 280 



Specular iron ore, a very abundant ore, including tlie hematite, 

 the calcareous and specular, as also the clay and jaspery iron 

 ores, red hematite, has a specific gravity of 4.5, and a cubic 

 foot weighs 290 



Wrought iron, a cubic foot weighs ' 487 



Limestone hydraulic has a specific gravity of 2.7, and a cubic 



foot weighs 150 



Magnesian, is now in gi*eat demand for producing very hard 



cement, specific gravity 2.5, and a cubic foot weighs 130 



Manganese, binoxyde of, or pyrolusite, has a specific gravity of 



4.8, and a cubic foot weighs 294 



Bog or wad, an inferior quality of the above, has a specific 



gravity of 3.5, and a cubic foot weighs 217 



Mountain copper, or malachite, or green carbonate of copper, an 



ornamental stone from Siberia, Australia, and United States, 



has a specific gravity of 4.0, and a cubic foot weighs 248 



Muscovite, or mica, a mineral destined to be ever in much 



demand for the arts and large de]'»osits of which are found in 



several States, has a specific gravity of 2.8, and a cubic foot 



weighs 160 



Novaculite, or whetstone, a valuable mineral from Arkansas, 



North Carolina, etc., has a specific gravity of 3.0, and a cubic 



foot weio-hs ,- 186 



Ochre, extensive beds exist all over the United States ; the 3'el- 



low and brown ochre have a specific gravity of 3.5, and a 



cubic foot weighs 217 



Platinum, the specific gravity of the metal and ores is from 16 



to 19, and a cubic foot weighs, an an average 1,116 



Porcelain clay, commonl}^ called China clay, distributed all over 



the United States, has a specific gravity of 2.0, and a cubic 



foot weighs 140 



Pyrites iron, or bisulphide of iron, pyrrliotine, or magnetic 



pyrites, a simple sulphide of iron, all have an average specific 



gravity of 4,5, and a cubic foot weighs 280 



