CHEMISTRY. 



Elements Potash, according to the experiments of Mr Davy, 



is composed of about 

 Chemutrr. r,^ 



86 potassium, 



14 oxygen. 



Utry. 



Coiutitn- 

 cr.ts of 

 potash. 



100 



According to Thenard and Gay-Lussac, it is com- 

 posed of 83.371 potassium, 

 16.629 oxygen. 



Soda, 



how pro- 

 cured. 



Its proper- 

 ires. 



Its proper- 

 tie*. 



Codi posi- 

 tion of 



100 



SECT. III. Of Soda. 



Soda, called also fossil or mineral alkali, is found 

 in large quantities ready formed in the earth. It 

 may be obtained also from the ashes of the different 

 species of saliolii and other marine plants. The pro- 

 cess is the same as that for procuring potash. 



When pure, it has a very strong resemblance to 

 potash in most of its properties. 



Its colour is greyish white, and it agrees with pot- 

 ash in its taste, smell, and action on animal bodies. 

 Its specific gravity is 1.336. 



Heat produces the same effects on it as on potash. 

 In the open air, it absorbs water and carbonic acid, 

 but it does not become liquid as potash does. After 

 assuming the state of a paste, it soon dries again, and 

 crumbles to powder. 



It dissolves in water like potash, and may be ob- 

 tained crystallized. The action of oxygen, of the 

 simple combustibles and incombustibles, is similar to 

 their action on potash. The same remark applies to 

 the metals and their oxides. 



Like potash, it is a compound of oxygen and a pe- 

 culiar metal, to which Mr Davy, the discoverer, has 

 given the name of sndium. It may be decomposed 

 precisely in the same way as potash. 



Sodium is a white metal like silver, solid, but very 

 malleable, and so soft, that pieces may be welded to- 

 gether by strong pressure. At 120, it begins to 

 melt ; and is completely fluid at 180. It is not vo- 

 latilized in a red heat strong enough to melt plate- 

 glasa. It conducts electricity and heat in the same 

 manner as potassium. Its specific gravity is 0.934-8. 



Its affinity for oxygen is similar to that of potas- 

 sium. When exposed to the air, it is soon covered 

 with a crust of soda; but as that alkali does not de- 

 liquesce, the nucleus is not so soon destroyed as hap- 

 pens to potassium. Hydrogen gas does not dissolve 

 it. Hence no combustion takes place when sodium 

 is thrown upon water, though it rapidly decomposes 

 that liquid. 



When fused with dry soda in certain quantities, 

 there is a division of oxygen between the soda and 

 the base, and a protoxide of sodium is formed, of a 

 deep brown colour. It is capable likewise of absorb- 

 ing an additional dose of oxygen, and of forming a 

 peroxide. 



It burns like potassium in chlorine. It combines 

 with phosphorus, sulphur, and the metals, like potas- 

 sium. From the experiments of Mr Davy, it appears 

 that soda is composed of 



Sodium 78 

 Oxygen 22 



100 



According to Thenard and Gay-Lussac, it is com- E'<-ments 

 posed of Sodium 7-1.63 of 



Oxygen 25.37 Ctemisfrjr. 



100 



Thus it appears, that the two fixed alkalies are me- 

 tallic deutoxides. It is very probable that ammonia is 

 likewise an oxide, though the metallic base of which 

 it consists has not yet been obtained in a separate 

 state. 



CHAP. II. 



Of the Alkaline Earths. 



The term earth, in chemistry, is applied to all Earth eu 

 substances possessing the following properties. plained. 



1. Insoluble in water, or at least becoming insolu- 

 ble when combined with carbonic acid. 



2. Little or no taste or smell, at least when com- 

 bined with carbonic acid. 



3. Fixed, incombustible, and incapable, when pure, 

 of being altered by the fire. 



4. A specific gravity not exceeding 4.9. 



'5. When pure, capable of assuming the form of a 

 white powder. 



6. Not altered when heated with combustibles. 



The earths have been divided into two classes, 

 namely, alkaline earths, and earths proper. The al- 

 kaline are four in number, namely, lime, magnesia, 

 barytes, aud strontian. 



SECT. I. Of Lime. 



Lime has been known from the remotest ages. It Lime, 

 abounds in every part of the earth, constituting im- 

 mense ranges of rocks and mountains. It may be 

 obtained by burning those crystallized limestones 

 called calcareous spars, or certain white marbles. 

 Oyster shells, also, when burnt, yield it nearly pure. 



Pure lime is white, moderately hard, but easily re- tts proper- 

 duced to powder. Its taste is acrid like that of the *' 

 fixed alkalies, and it in some measure corrodes those 

 animal bodies to which it is applied. Its specific 

 gravity is 2.3. It tinges vegetable blues green, and 

 at last renders them yellow. It does not melt in the 

 most violent heat that can be applied. 



When water is poured upon it, the lime swells and Hydrate pf 

 falls to pieces, and so much heat is evolved as to eva- l'nw 

 porate a portion of the water, and even to set fire to 

 combustible substances with which it happens to be 

 in contact. This process is called slacking the lime. 

 A portion of the water combines with the lime, and 

 becomes solid. Hence the cause of the heat evolved. 

 Slacked lime is composed of 3 parts lime and 1 wa- 

 ter. It has been called hydrate of lime. 



The difference between limestone and lime was first 

 ascertained by Dr Black. Limestone is lime com- 

 bined with carbonic acid. By burning it, the car- 

 bonic acid is driven off, and the pure lime remains. 



When lime is exposed to the open air, it gradually 

 attracts moisture, falls to powder, and, becoming sa- 

 turated with carbonic acid, soon resumes its original 

 state of limestone. 



Water dissolves less than 0.002 parts of its weight I.irae- 

 of lime. The solution is called lime-water. It is watM - 



