OBDER IV. TETABTO-PBISMATIC VITRIOL-SALT. 45 



the present place it seems to be the best, to describe one 

 of the varieties most generally occurring, together with 

 the angles as given by HAUY, in order to enable the stu- 

 dent to compare this crystal with others he should meet 

 with in nature. 

 This variety is represented Fig. 83. The incidence 



of P to M is = 109 32'; 



of P to T = 128 27'; 



ofM to T = 149 2'; 



of to T = 149 42"; 



of r to M = 126 11'; 

 of r to T = 109 47'; 

 of u to P = 126 11'; 

 of u to M = 124 17'. 



of n to M = 154 2(K; 



2. The tetarto-prismatic Vitriol-salt consists of 



Oxide of Copper 32-13. 



Sulphuric Acid 31-57. 



Water 36-30. BERZELIUS. 



It is Cu S 2 + 10 Aq = 29-9 Oxide of Copper : 32-3 

 Sulphuric Acid : 37*8 Water, according to MITSCHEH- 

 LICH. Very often sulphate of copper is contained in dif- 

 ferent proportions in the crystals of hemi-prismatic Vitriol- 

 salt ; the forms of the latter nevertheless are not affected 

 by this admixture, except that they more commonly pre- 

 sent the simple varieties, as, for instance, that of Fig. 44. 

 It is easily soluble in water, and gives a blue solution. A 

 polished surface of iron is covered with a film of metallic 

 copper, if dipped into this solution. 



3. This salt, like the preceding one, owes its existence 

 to the decomposition of other minerals, particularly of py- 

 ramidal Copper-pyrites, and is often produced by various 

 chemical processes. It is found dissolved in several wa- 

 ters, partly issuing from mines, and which have received 

 the name of waters of Cementation. 



4. Its chief localities are the Rammelsberg near GosJar, 

 Neusohl in Hungary, Anglesea in England, Wicklow in 

 Ireland, Fahlun in Sweden, the isle of Cyprus, &c. 



5. As it occurs in nature, it requires first to be puri- 

 fied, before it can be employed in the arts, where it is used 

 in dyeing, in printing of cotton and linen, &c. The oxide 

 of copper, separated from its acid, is likewise used in painting. 



