GRA 



GRA 



gas-house liquor, salt, a watering of 

 whale oil soap, and similar bodies, 

 taking care not to destroy the herbage. 



GRAYWACKE. Gray rock. An 

 old geological term for the gray tran- 

 sition rocks ; as gneiss, mica, slate, 

 &c. 



GRAVEL. A geological forma- 

 tion or soil, consisting of rolled peb- 

 bles, loosely interspersed, more or 

 less abundantly, in a sandy or clayey 

 medium. It is of every degree of 

 fineness, chemical composition, and 

 value in farmmg. Those gravels 

 containing siiicions pebbles chiefly, 

 and of a Targe size, are nearly unfit 

 for tillage, and the value increases 

 with the presence of slates, gran- 

 ites, hornblende, mica, marl, and clay. 

 They are usually very porous, drain- 

 ing water off rapidly, and cannot be 

 of much value, unless incumbent on 

 a subsoil that holds water at some 

 little depth. If the gravel be fertile, 

 it is usually warm and best adapted 

 for roots. Stiff marls, burned clay, 

 and an abundance of vegetable mat- 

 ter are to be used as manures. 



Gravel is well adapted for forming 

 walks in gardens and the surface of 

 roads. 



GRAVEL. In farriery, the forma- 

 tion of hard calculi or stones in the 

 bladder, or of a sandy sediment. 



GRAVEOLENT. Fetid, having a 

 strong odour. 



GRAVES, GREAVES. Mem- 

 branous matter left as refuse by the 

 tallow-melter ; it is used for feeding 

 dogs, and given to poultry. Graves 

 contains a large amount of fat, and 

 is admirably adapted for fattening 

 hogs, &c. ; it has been used, also, as 

 a manure ; 200 pounds interspersed j 

 in stable manure may be added to 

 the acre ; but the most economical 

 plan will be to compost it in the nitre i 

 bed. It is a nitrogen manure, 100 

 pounds yielding about 13 pounds of! 

 ammonia, and being equal, in this 

 respect, to I^ tons of farm-yard ma- | 

 nure. The presence of sulphur and [ 

 phosphorus, besides bone earth, also 

 constitute it a manure applicable to 

 all rich crops ; as corn, wheat, to- i 

 bacco, &c., the only consideration 

 350 



being the economy of using so high- 

 priced an article. See Manures. 



GRAVID. Pregnant. 



GRAVIMETER (from gravis, 

 heavy, and /lerpov, a measure). See 

 Hydromclcr. 



GRAVITATION, GRAVITY. 

 The tendency that masses have to 

 approach each other ; also called at- 

 traction of gravitation. The gravity 

 of a body is therefore the attraction 

 it extends towards other bodies ; it 

 increases with the bulk, density, and 

 nearness of bodies, being directly as 

 their density and mass, and inverse- 

 ly as the squares of their distances. 

 Weight, and the descent of all bodies 

 towards the earth's surface, is an ef- 

 fect of the earth's gravity, or terres- 

 trial gravitation. 



GRAVITY, SPECIFIC. The ra- 

 tio of the weight of any solid or liquid 

 to the weight of an equal bulk of pure 

 water at 62' Fahreniieit. The spe- 

 cific gravity of gases is the ratio to 

 the weight of an equal volume of air 

 at the same temperature. If the sol- 

 id be lighter than water, the measure- 

 ment is made more indirectly. 



Hoio taken. — The specific gravity 

 of solids is taken by first weighing a 

 piece in air, and then weighing it im- 

 mersed in pure water, and dividing 

 the weight in air by the loss of weight 

 in water. Fluids are examined either 

 by filling a bottle known to contain 

 precisely 1000 grains of pure water, 

 up to a certain mark, and setting 

 down the weight, irrespective of that 

 of the bottle, as the specific gravity. 

 This is called the 1000 grain bottle. 

 Or an instrument called a hydrometer, 

 gravimcter, or areometer is immersed 

 in the fluid, and sinks to a certain 

 mark, which indicates the specific 

 gravity or density (see Hydrometer). 

 The gravity of gases is taken by first 

 exhausting a glass vessel of air by 

 the air pump, and then introducing 

 the particular gas, the weight of 

 which, irrespective of the glass, will 

 be the second proportional of the fol- 

 lowing series : As the weight of air 

 is to that of the gas, so is 1 to the 

 specific gravity of the gas ; that is, 

 the weight of the gas divided by that 



