GREEN IRON ORE 



737 



vincial miner's term. Although at one period, the term grauwacJce or greywacke, -was 

 employed to include the Cambrian and Silurian slates, the term has now nearly dropped 

 out of the geological nomenclature. 



GRAVE-WAX. A familiar term for adipocere. See ADIPOCERE. 



GRAVITY. The term usually applied to the action of the earth's gravitation. 



GRAVITY, SPECIFIC. The specific gravity of a body is represented by the 

 ratio which the weight of a given volume of the body bears to the weight of an equal 

 volume of a certain substance chosen as a standard of comparison. Water is the 

 standard for solids and liquids, and air the common standard for gases, but modern 

 chemists frequently refer the specific gravity of gases to hydrogen as unity. If, there- 

 fore, the specific gravity of platinum is stated to be 19'5 (water= 1), or 19500 (water 

 = 1000), it is simply meant that a given bulk say a cubic inch of platinum will 

 weigh 19 times as much as a cubic inch of water weighs. In like manner the specific 

 gravity o"f oxygen is said to be 1-1056 (air = l), or 16 (hydrogen = 1 ), by which is 

 meant that a certain volume of oxygen weighs 1 Q times greater than the same 

 volume of air, or 16 times as much as an equal bulk of hydrogen; all the weights 

 being determined under like conditions of temperature and pressure. Specific gravity 

 is sometimes called ' relative weight,' and is commonly regarded as the same thing as 

 ' density.' For a description of the several methods by which the specific gravity of any 

 body, either solid, fluid, or aeriform, may be determined, we must refer to Watts's 

 ' Dictionary of Chemistry,' or to any works treating of the manipulatory details of 

 physics or chemistry. The following Table may be found useful : 



Table of Specific Gravities. 



GREBE. A water-bird, Podiceps cristatus, the great crested or tippet grebe. 

 It is about the size of a goose, and a native of England, being found in the fens of 

 Shropshire, Cheshire, and Lincolnshire, where they are called gaunts. The bird, which 

 is valued for the plumage of its breast, so much admired by ladies for muffs, and 

 used for trimmings, is a large Swiss and Central European species. 



GREEN EARTH. An earthy mineral occurring in cavities in amygdaloidal 

 melaphyres, especially at Monte Baldo, near Verona, whence it is procured for use as 

 a pigment, being sold under the name of Terre verte de Verone. 



GREEN EBONY of Jamaica. This is a wood of a brown-green colour. It is 

 derived from the Amei*imnum Ebenus, and is used in turnery and for marquetry-work. 

 See MARQUETRY ; PARQUETRY. 



GREENHEART. A wood brought from Jamaica and Guiana, the produce of 

 the Laurus chloroxylon. It is used in shipbuilding. Bancroft, in his ' Guiana,' thus 

 describes it : ' The Sipiera or Greenheart tree is in size like the locust-tree, about 60 

 or 70 feet high ; there are two species, the black and the yellow, differing only in the 

 colour of their bark and wood.' 



GREEN IRON ORE. A native phosphate of iron. See DUFBENITB, 



VOL. II. 3 B 



