HELIOGRAPHY 



797 



HEAVE a miner's term, expressing the dislocation of a lode. See FAULT. 



HEAVY-SPAR (Spatk pcsant, Fr. ; Schwerspath, Ger.), is an abundant mineral, 

 which accompanies veins of lead, silver, mercury, &c., but is often found, also, in large 

 masses. Its colour is usually white, or flesh coloured. It varies from translucent to 

 opaque. It belongs to the trimetric system, but occurs in many crystalline forms, 

 of which the cleavage is a right rhomboidal prism. It is met with also of a fibrous, 

 radiated, and granular structure. Its sp. gr. varies from 4'1 to 47; H = 2'6 to3'5. It 

 has a strong lustre, between the fatty and the vitreous, sometimes pearly. It melts 

 at 35 Wedgw. into a white opaque enamel. It is a sulphate of baryta ; its constituents 

 being 65*67 baryta, and 34'33 sulphuric acid; but it is sometimes rendered impure 

 by oxide of iron, silica, carbonate of lime, and alumina, and commonly by sulphate of 

 strontia. It is not acted upon by acids ; decrepitates before the blowpipe ; and is 

 difficultly fusible, or only on the edges. In the inner flame it is reduced to a sulphuret, 

 and the globule when moistened smells slightly hepatic. It is decomposed by calci- 

 nation in contact with charcoal at a white heat, into sulphide of barium ; from which 

 all the baryta-salts may be readily formed. Its chief employment in commerce is for 

 adulterating white-lead ; a purpose which it readily serves on account of its density. 

 Its presence here is easily detected by dilute nitric acid, which dissolves the carbonate 

 of lead, and leaves the heavy-spar. It is also a useful ingredient in some kinds of 

 pottery, and glass. 



The following were the quantities of barytes, both carbonate and sulphate, returned 

 to the Mining Record Office, from ths mines of Great Britain, and reported in Hunt's 

 Mineral Statistics' for 1872: 



Shropshire 



Northumberland 



Derbyshire 



Snailbeach (Sulphate) . 



Snailbeach (Carbonate . 



Weston (Sulphate) . . 



Wortherton (ditto) . 



Fallowfield (Carbonate) . 



Settlingstones (Carbonate) 



Cow Green 

 Cumberland . . Alston Moor (Carbonate) 



Foree Craig . 



Buxton . . , 



Golconda (Carsington) . 



Grey Mare, "Wirksworth . 



Eantor, ditto 



Croft Doghole, Middleton 



Bradwell, ditto 



Moors near Blakewell 



Longstone Eake 



Salad Hole . 



MiUer's Dale . 



Castleton 



Monsal Dale . 



Eyham .... 



Wensley and Stanton 



Wardlow 

 Montgomeryshire . Van Consols (Sulphate) . 



Tons. cwt. qrs, 



414 1 



2 U 3 



384 



1,483 



2,001 18 



1,695 



800 



135 9 



600 



. *. d. 



310 10 



1 19 



288 



1,112 



1,500 



1,271 



17 



101 11 9 



600 



2,012 17 1 



1,609 12 9 



356 



Total ascertained production . 9,092 17 



26 

 7,078 13 6 



Derbyshire, the Isle of Arran, and Ireland produced some sulphate of baryta which 

 has not been given in the above return. 



The term Cawk has been applied to the opaque massive variety, of an earthy 

 appearance, and dirty-white colour, which is found in Derbyshire and Staffordshire. 



HECKXiE (Scran, Fr. ; Hcchel, Ger.) is an implement for dissevering the filaments 

 of flax, and laying them in parallel stricks or tresses. See FLAX. 



HEIiXCXlff. A crystalline alkaloid produced by the oxidation of salicin, the bitter 

 principle of the poplar and willow. 



HEXiXOGR APHY was the name given by M. Niepce to his process for obtaining, 

 through the agency of the solar rays upon plates of metal or glass covered with resins, 

 the impression of external objects. The process has been employed of late years in 

 preparing lithographic stones, and steel or copper plates, for receiving photographic 

 impressions, which might be subsequently printed from. The name Heliography is a 

 far more appropriate one than Photography ; but the latter has become top permanently 

 fixed in our language to leave any hope of our returning- to the former. See PHOTO- 



OEAPHY. 



