HARMALA RED 



783 



use.' Steel plates are hardened occasionally by allowing water to fall on them when 

 hot 



Case-hardening is the process by which wrought iron is first converted exteriorly 

 into steel, and is subsequently hardened to that particular depth, leaving the central 

 parts in their original condition of soft and fibrous iron. The principal agents used 

 for case-hardening are animal matters, as the hoofs, horns, bones, and skins of animals. 

 The prussiate of potash, which contains a compound of carbon and nitrogen, is also 

 employed for case-hardening. In principle its action is the same as that of the animal 

 substances. The iron is heated in the open fire to a dull red, and the prussiate is 

 either sprinkled upon it or rubbed on in the lump ; it is returned to the fire for a few 

 minutes, and immersed in water. In the volume of Lardner's ' Cyclopaedia,' on Iron 

 and Steel, edited by Eobert Hunt, the subjects of hardening and tempering are treated 

 in a practical manner. See IRON. 



HARDNESS. (Durete, Fr. ; Harte, FestigJceti, Ger.) A hard body will scratch 

 one that is softer than itself. This method of determining the hardness of minerals 

 is employed by mineralogists. A good steel file is commonly used for trying the re- 

 spective hardness of minerals. 



Mohs introduced a scale of hardness which shows the gradual increase in hardness 

 through 10 minerals : 



6. Feldspar (orthoclase ; white cleav- 



able variety). 



7. Quartz; transparent. 



8. Topaz ; ditto. 



9. Sapphire ; cleavable varieties. 

 10. Diamond. 



1. Talc ; common laminated light green 



variety. 



2. Gypsum ; crystallised variety. 



3. Calcite; transparent variety. 



4. Fluor spar ; crystalline variety. 



5. Apatite ; transparent variety. 



The following table, compiled by Dr. Ure for the early editions of his Dictionary, 

 will still be found very useful as representing, relatively, the hardness of the mineral 

 named, although the numbers which express the degree of hardness do not agree with 

 the scale of Mohs : 



One of the most ready means of discriminating between different kinds of precious 

 stones is to be found in their different degrees of hardness, coupled with their specific 

 gravities. These are given in the article on GEMS. In many of the mineralogical 

 articles in this Dictionary, the letter H is used as an abbreviation of ' hardness.' 



HARDWARE. Under this term are comprehended the articles manufactured of 

 any of the baser metals. See these respectively. 



HARE. The common hare (Lepus timidus) not only furnishes an article of food, 

 but the skin is used as a fur, and was formerly employed to a large extent in making 

 the felt bodies of hats. 



HARE WOOD. See SYCAMORE. 



HARICOTS. The seeds of certain species of Phaseolus, or beans. 



HARlKAXiA RED. A red-colouring matter, obtained from the seeds of 

 Peganum Harmala, a plant found in the Crimea. It is obtained by digesting the seed 

 in alcohol for some days. This colouring matter unites with acids, forming red-salts, 



