13AS 



fcAS 



tains these concretions are collected into 

 larger groupes, of which many together 

 form a hill or a mountain. Sometimes 

 the columns are articulated, and the 

 joints have convex and concave faces. 

 The specific gravity is by Bergman put 

 at 3.0 : by Brisson at 2.86 : and by Kir- 

 wan at 2.98. Before the blow-pipe it ea- 

 sily melts without addition into an opaque 

 black glass. By analysis the constituent 

 parts have been brought out differently 

 by different chemists, but according to 

 Klaproth they are as follow : 



Silica 44.50 



Alumina .... 16.75 

 Oxide of iron . . 20.00 



Lime 9.50 



Magnesia .... 2.25 

 Oxide of Manganese 0.12 



Soda 2.60 



Water 2.00 



97,62 



It is found in vast mountainous beds, 

 in most parts of the world, and almost al- 

 ways accompanies coal. The island of 

 Staffa, on the western coast of Scotland, 

 is entirely composed of basaltic pillars : 

 the Giants' Causeway, on the coast of 

 Antrim, in Ireland, is a huge pavement of 

 straight pillars, running to an unknown 

 distance in the sea : the promontory of 

 Fairhead, a little further to the north, ex- 

 hibits a continued range, about a mile 

 long, of columns 250 feet in height, and 

 from 10 to 20 in diameter, being the larg- 

 est yet known. 



Basalt is employed as a building stone 

 and touch stone ; as a flux for certain ores 

 of iron; in glass manufactures; in mak- 

 ing the common green glass. The vesi- 

 cular varieties are employed for mill- 

 stones. Owing to its great hardness, the 

 ancients, who were acquainted with its 

 indestructibility, executed several fine 

 works in it ; many of which are preserved 

 in great perfection to this day. The 

 origin and formation of basalt are much 

 controverted. Bergman introduced the 

 theory of its aqueous formation ; and to 

 this Jameson inclines, from observing that 

 the strata which are in contact with basalt 

 generally exhibit appearances incompa- 

 tible with the action of fire. Since the 

 time of Bergman, the two theories have 

 nearly equally divided the mineralogical 

 world. The Swedes, Germans, and Wer- 

 nerians in Britain, maintain the aqueous 

 theory : they have shewn basalt resting 

 upon and alternating with strata of ac- 



knowledged aqueous origin; they have 

 discovered shells and vegetable remains 

 imbedded in its substance ; they have 

 found its cavities filled by sihcious nodules 

 containing water ; they have melted ba- 

 salt in their furnaces, and have found it to 

 produce glass; they have moreover shewn 

 that the lava of Vesuvius and Etna differs 

 in many important particulars from 

 basalt ; and they have pointed out the 

 prismatic structure in many substances, 

 which are not supposed to have under- 

 gone the action of fire. 



The French, the Italians, and Dr. Hut- 

 ton and his disciples in this country, main- 

 tain the igneous origin of basalt ; in de- 

 fence of their system they have shewn 

 the prismatic structure of some undoubt- 

 ed Italian lavas : they have shewn beds of 

 coal charred by the contact of dykes of 

 basalt, and the forcible disruption, incur- 

 vation, and induration of argillaceous 

 strata, when pierced through by means 

 of this substance. Sir James Hall has 

 proved that basalt, after it has undergone 

 the vitreous fusion, may be made to as- 

 sume a perfect stony appearance : and 

 Mr. Watt has demonstrated, by experi- 

 ment, that basalt may, by the medium of 

 fire, acquire those peculiarities of struc- 

 ture that cannot readily be explained by 

 the aqueous theory. 



BASE, in architecture, is used for any 

 body which bears another, but particu- 

 larly for the lower part of a column and 

 pedestal. The base of a column is that 

 part between the shaft and the pedestal, 

 if there be any pedestal ; or if there be 

 none, between the shaft and the plinth, 

 or zocle. The base is different in the dif- 

 ferent orders. See ARCHITECTURE. 



BASE, in chemistry, a term used to de- 

 note the earth, the alkali, or the metal 

 of which a salt is formed in union with 

 oxygen. It admits, however, of a more 

 general application. The name of gas 

 is given to any aeriform fluid, which 

 consists of some substance combined with 

 caloric, and capable of existing in an ae- 

 riform state under the usual pressure and 

 temperature of the atmosphere : thus ox- 

 ygen gas consists of oxygen, which is the 

 base, and caloric. The alkalies, earth, 

 and metals, are called salifiable bases or 

 radicals, and the acids salifying princi- 

 ples. The name of each salt is composed 

 of that of the acid and the salifiable base : 

 thus sulphate of potash consists of sul- 

 phuric acid and potash, which is the 

 base. 



BASE, in fortification, the exterior side. 

 of the polygon, or that imaginary line 



