CHEMISTRY. 



Element* 



of 

 Chemistry. 



Retina t- 



plialtum. 



tinues afterwards of the consistence of tar. In that 

 state it is soluble in oils. It burns with a bright 

 flame and bituminous smell. 



4. Retinasphahum has hitherto been found only 

 in Derbyshire, accompanying Bovey coal. Mr Hat- 

 chett discovered its nature. It has a pale brown 

 ochre yellow colour, is very brittle, and breaks with 

 a vitreous fracture. Its specific gravity is 1.135. 

 When heated, it melts, smokes, and burns with a 

 bright flame, and emits a fragrant odour. It is inso- 

 luble in water, but partially soluble in alcohol, pot- 

 ash, and nitric acid. It is composed of 



Resin, 55 



Asphaltum, 41 



Earths, 3 



99 



Pic-coaL 5. Pit-coal, one of the most useful of all tha mi- 



neral productions, may be distinguished into three 

 kinds. 1. Those that still contain vegetable princi- 

 ples, strictly so called, and thus give evident marks 

 of their origin. Some yield extractive, others resin, 

 besides charcoal and bitumen, which constitute the 

 greatest part of their contents. The term bromn 

 coal, from their colour, has been applied to the great- 

 er number of coals belonging to this set. 2. Black 

 eoal. In them no vegetable principle can be detect- 

 ed, they are composed ot bitumen and charcoal in 

 various proportions, and are usually mixed with more 

 or less of earthy matter. 3. Glance coal. In this 

 et no vegetable principle, nor even bitumen, is to be 

 found. The coal consists of charcoal pure, or con- 

 taminated with some earth. These coals have a great 

 deal of lustre. They are heavy, and burn without 

 emitting any flame or smoke, and only when heated 

 to redness. 



DIVISION II. 

 ON SECONDARY COMPOUNDS. 



Secondary BY the term secondary compound, is meant a com- 

 bination of primary compoundt with each other. 

 Thus acids combine with alkalies and form sails ; 

 earths combine with fixed alkalies and form glass ; 

 oils combine with fixed alkalies and form soap. The 

 secondary compounds, as far as we are at present 

 acquainted with them, may be arranged under the five 

 following classe- : 



1. Combinations of earths with each other, and 

 with metallic oxides. 



2. Combinations of earths with alkalies. 



3. Combinations of acids with alkalies, earths, and 

 metallic oxides. 



4. Combinations of sulphureted hydrogen with al- 

 kalies, earths, and metallic oxides. 



5. Combinations of oils with alkalies, earths, and 

 metallic oxides. 



These combinations may be distinguished by the 

 following titles: 1. Combinations of earths; 2. 

 Glass ; 3. Salts ; 4. Hydrosulphurets ; 5. Soaps. 



TOL. VI. TABT I. 



CHAP. I. 



Elements 



of 

 Chemistry. 



Of Combinations of Earths. 



THIS subject is in some measure new, and has been Combiua- 

 but imperfectly investigated. The following obser- t '" 9 of 

 vations are all that can be offered : 



1. The earths require so violent a heat to melt 

 them, that they are capable of resisting the most in- 

 tense fires that we can raise. But in several cases 

 the fusion is much facilitated by mixing various earths 

 together. Thui alumina, in a pure state, is infusible, 

 and so is a mixture of alumina and silica, or pure clay. 

 But when lime is added to this substance, it melts 

 with comparative facility. The oxide of iron also 

 acts as a solvent when mixed with other earthy bo- 

 dies, and greatly facilitates their fusion. 



2. The three alkaline earths, lime, barytes, and 

 strontian, resemble each other in their disposition to 

 unite with the other earths. Like the alkalies, they 

 combine with alumina and silica, but shew no affini- 

 ty for magnesia nor for each other. 



3. Magnesia has a marked affinity for alumina, but 

 for none of the other earths. When magnesia and 

 alumina are present together in solutions, alkalies 

 throw them down in combination. 



4. Alumina has an affinity for all the alkaline 

 earths. It has also an affinity for silica. These 

 two earths are frequently found combined in na- 

 ture. 



5. Silica has an affinity for the alkaline earths, for 

 alumina, and for ziicoma. Silica enters into fusion 

 with all the earths hitherto tried except alumina. 



6. Several of the earths are capable of combining 

 likewise with metallic oxides. Hitherto only six 

 metals in the state of oxides have been found native 

 combined with earths. These are, 1. chromium ; 2. 

 nickel ; 3. copper ; 4. zinc ; 5. manganese ; G. iron. 



Chromium constitutes the colouring matter of the 

 ruby, in which mineral it is combined with alumina 

 and magneaia. Nickel has been found only in one 

 mineral, the chrysoprase, to which it gives a green co- 

 lour. The same remark applies to copper, which 

 has been found only in the smaragdite, and in a very 

 small proportion. Zinc is sometimes found combi- 

 ned with silica in the mineral called calamine, which 

 is frequently merely an oxide of zinc. The oxide of 

 manganese is a very frequent ingredient in dark co- 

 loured stones, as schorl, garnet, &c. It is found also 

 combined with barytes. 



But it is the oxide of iron which constitutes by 

 far the most common metallic constituent of mine- 

 rals. No less than seven distinct colours, besides 

 various shades, have been observed in minerals con- 

 taining iron. These are white, black, green, blue, 

 red, yellow, brown. 



Tine oxides of iron melt when heated with barytes, 

 lime, alumina, or silica, when they exceed the propor- 

 tion of earth considerably. They render mixtures of 

 silica and alumina fusible at a very low heat, 



