80 



CHEMISTRY. 



The composition of common alum was first ascer. 

 tained by Vauquelin. It crystallizes in regular octa- 

 hedrons. It is white, and semitrausparent. Its taste 

 is sweetish and astringent, and 1t reddens vegetable 

 blues. It dissolves in about 16 parts of cold water. 

 In a gentle heat, it undergoes the watery fusion, and 

 by continuing the heat, it loses about 44 per cent, of 

 water, and is called calcined or burnt alum. In a 

 violent heat, a portion of the acid is converted into 

 sulphurous acid, and oxygen gas. This salt, accord- 

 ing to the analysis of Vauquelia, is usually com- 

 posed of 



Sulphuric acid, 30.52 



Alumina 10.50 



Potash, ..... 10.40 



Water 48.58 



100.00 



Alum sometimes contains a little sulphate of iron 

 mixed with it, which injures its qualities as a mordant. 

 The ntlphatex, or two first varieties, may be form- 

 ed by boiling alumina in a solution of alum. They are 

 tasteless powders, insoluble in water, and not altered 

 by exposure to the air. 



Sp. 10. Sulphate of Yttria. This salt crystallizes 

 in flat six-sided prisms. It is not altered by exposure 

 to the air. Its taste is astringent and sweet. It has 

 an amethyst red colour, and dissolves in about 30 

 parts of cold water. At a red heat it is perfectly de- 

 composed. 



Sp. 11. Sulphate of Glucina. This salt is colour- 

 less. It crystallizes in needles. Its taste is very 

 sweet, and somewhat astringent. It is very soluble 

 in water, and the solution does not readily crystallize. 

 When heated, it undergoes the watery fusion, and in 

 a red heat, is completely decomposed. 



Sp. 12. Sulphate ofZirconia. This salt is usually 

 in the form of a white powder ; though it may be 

 obtained also crystallized in needles. It is tasteless, 

 and insoluble in water ; not altered by exposure to 

 the air, and easily decomposed by heat. 



Sp. 13. Sulphate of Lime. This salt occurs na- 

 tive, and is distinguished by the names of gypsumand 

 tclenite. It is found crystallized in octahedrons, six- 

 sided prisms, and in lenses. It has little or no taste. 

 It dissolves in about 460 parts of cold water. It is 

 not altered by exposure to the air. It dissolves in 

 sulphuric acid. When heated, it loses its water of 

 crystallization. When mixed with a little lime, it is 

 much used under the name of plaster of Paris, for 

 forming casts, moulds, &c. 



Sp. 14. Sulphate of Baryles . This salt is found 

 native, and distinguished by the names of ponderous 

 tpar, heavy spar, baroselcnitc. It occurs crystallized 

 in tables, with bevelled edges, in four sided prisms, 

 &c. It is white, tasteless, insoluble in water, but so- 

 luble in hot sulphuric acid. It melts, when strongly 

 heated, into a white opake globule. When made into 

 a cake with flour, and heated to redness, it is phos- 

 phorescent. 



Sp. 1~>. Xitli>liate (if Strontian. This salt, like the 

 preceding, occurs native in considerable quantity. It 

 i* crystallized in rhomboidal prisms. It it white, 

 tasteless, insoluble in water, but soluble in hut sul- 

 phuric acid. In most of its properties it resembles 



the preceding salt, but its specific gravity is much K' 

 le. The specific gravity of sulphate of barytes is of 

 at least 4.3, while that of sulphate of strontian does Cl 

 not exceed 3.66. ~.~" 



The following table exhibits the composition of 

 the different sulphates, as far as it has been ascer- 

 tained. 



GENUS VIII. Sulphites. 



The sulphites may be formed by passing a current Sulphites, 

 of sulphurous acid gas through water, holding the 

 different bases in solution or suspension. They have 

 a disagreeable sulphureous taste. When heated, they 

 emit sulphurous acid and water, and at last sulphur, 

 and are converted into sulphates. When they are ex- 

 posed to the air in a state of solution, they are also 

 gradually converted into sulphates. 



Sp. 1. Sulphite ofPotush. This salt crystallizes 

 in rhomboidal plates, white, and semitransparent. Its 

 taste is penetrating and sulphureous. It dissolves in 

 its own weight of cold water. In the air it loses 

 about two per cent, of its weight, and is very slowly 

 altered ; at least in six months it still contained nearly 

 the usual proportion of sulphurous acid. Nitric acid 

 speedily converts it into sulphate of potash. 



Sp. 2. Sulphite of Soda. This salt crystallizes in 

 flat four sided prisms. It is white and transparent. 

 Its taste is cool and sulphureous. It dissolves in four 

 times its weight of cold water. In the air it efflo- 

 resces, and is converted into sulphate. When heated 

 it undergoes the watery fusion. 



Sp. .'i. Sulphite of Ammonia. It crystallizes in 

 six-sided prisms. Its taste is cool and penetrating, 

 and it leaves a sulphureous impression in the mouth. 

 It dissolves in its own weight of cold water. When 

 exposed to the air it attracts moisture, and is soon 

 converted into sulphate. When heated, a little am- 

 monia is disengaged, and the salt then sublimes in the 

 state of sit ;' r-.iitphitc of ammonia. 



Sp. 4. Sulphite of Magnesia. It crystallizes in 

 the form of depressed tetrahedrons. It is white and 

 transparent. Its taste is mild, but it leaves a sulphu- 

 reous impression in the mouth. When exposed to 

 the air, it becomes opake, and is very slowly convert- 

 ed into sulphate. It dissolves in 20 parts of cold wa- 

 ter. When heated, it becomes ductile like gum, and 

 loses 45 per cent, of its weight. 

 S 



