PHYSICAL SCIENCE. 



liii 



of oxygen gas I'llll, and that nitric acid is 

 formed by the union of one volume of the former 

 gas, with two and a half volumes of the latter ; 

 so that nitric acid is a compound of 1*75 of 

 azote, and five of oxygen by weight. 



Dr Priestley investigated the properties of 

 nitrous gas and protoxide of azote, and pointed 

 out the importance of the former in analysing 

 air. Davy subjected them to analysis, and ob- 

 tained pretty near approximations. The subject 

 was afterwards resumed by Dalton, and reduced 

 to its present state of simplicity by Gay-Lussac. 

 These gases are compounds of azote and oxygen ; 

 the former of 1*75 azote and two oxygen, and 

 the latter of 1'75 azote and one oxygen. 



Before the rise of scientific chemistry in Bri- 

 tain, the two alkalies, potash and soda, were 

 known, but they were not accurately distinguish- 

 ed from each other till Duhamel published his 

 dissertation on the subject in 1737. Lime had 

 been known from the beginning of the world ; 

 but its characters were first accurately pointed 

 out by Hoft'man. Magnesia had been discovered 

 about the beginning of the 1 8th century ; but 

 chemists were not acquainted with its true 

 character, and were in the habit of confounding 

 it with lime, till its properties, and the salts 

 which it forms, were accurately pointed out by 

 Black in 1765. Scheele discovered barytes in 

 1774, and strontian was recognised as a peculiar 

 substance as early as 1789 ; but its true nature 

 remained uncertain till Dr Hope published his 

 experiments on it in 1791, and Klaproth his a 

 few months earlier. Lithia was discovered by 

 Arfvedson in the year 1718. These seven bodies 

 were distinguished by the names of alkalies and 

 alkaline earths. Their properties were gradually 

 determined with accuracy, and the striking 

 r.nalogy which they have to each other was re- 

 cognised; but all the attempts made to deter- 

 mine their constituents were long unsuccessful. 

 At last Davy, in 1808, demonstrated that potash 

 is a compound of oxygen and a white very com- 

 bustible metal, to which he gave the name of 

 potassium ; and soda, of sodium and oxygen. He 

 was able, soon after, to show that lime, barytes, 

 strontian, and magnesia are also compounds of 

 metals and oxygen. And when lithia came to 

 be known, he showed that it also was a compound 

 of the metal lithium and oxygen. Thus it was 

 discovered that all the alkalies and alkaline 

 earths are metallic oxides. 



Alumina was known to the alchymists, but its 

 peculiar nature and properties were first deter- 

 mined by MargraafT in 1754^, and afterwards 

 more accurately by Scheele and Bergmann. 

 Glttcina was discovered in 1 798 by Vauquelin, as 

 a constituent of the beryl and emerald ; and 

 ytlria, in 1796, by Gadolin of Abo. Cerium was 



made known in 1804 by Klaproth, under the 

 name of ochroita, and a little after it was more 

 accurately examined by Berzelius and Hisinger, 

 who gave it the name of cerium. Zirconia was 

 discovered in the zircon, in 1789, by Klaprotli, 

 and afterwards in the hyacinth ; and thoritiv 

 was discovered by Berzelius in 1828, 



The analogy between these five bodies, and the 

 alkaline earths, was so strong, that as soon as 

 the nature of the latter was ascertained, chemists, 

 in general, inferred that the former also were 

 metallic oxides^ but several years elapsed before 

 this opinion was verified by experiment. At 

 last, a few years ago, (Erstedt discovered that if 

 alumina be intimately mixed with dry charcoal, 

 heated in a tube, and a current of dry chlorine 

 gas be made to pass over it, decomposition takes 

 place, and a pale greenish yellow substance 

 sublimes, which is a chloride of aluminum. 

 Wohler found that when this chloride is heated 

 with potassium it undergoes decomposition, the 

 chlorine uniting with the potassium, and the 

 aluminum being set at liberty. The aluminum, 

 or base of alumina, thus obtained, is a white 

 metal in grains, requiring a very high heat to 

 fuse it; probably malleable and permanent in 

 the air, or under water. When heated in air or 

 oxygen gas it takes fire, burns, and is converted 

 into alumina, by uniting with oxygen. 



Glucina was decomposed, and its basis gluci- 

 num obtained by the very same process. The 

 same remark applies to yttria. Glucinum and 

 yttrium have a strong resemblance to aluminum. 

 Cerium was first obtained in the metallic state by 

 Laugier in 1814, and zirconium by Berzelius in 

 1824. This last substance wants the metallic 

 lustre, and has a much stronger resemblance to 

 charcoal than to a metal. Thorina was reduced 

 precisely in the same way as alumina. Thorium 

 has also a striking resemblance to aluminum in 

 its properties. 



Thus it has been ascertained that all the fixed 

 alkalies, the alkaline earths, and the earths pro- 

 per, amounting altogether to thirteen, are 

 metallic oxides. 



The remaining simple bodies have been divid- 

 ed into two sets ; namely, acidifiable bases and 

 alkalifiable bases. The acidifiable bases are 

 eighteen in number. Of these there are two, 

 charcoal and sulphur, which were known to the 

 ancients. All the rest have been discovered by 

 the researches of chemists or chemical physicians. 

 The history of the discovery of hydrogen and 

 azote has been already given. 



Borax seems to have been known to Geber in 

 the eighth century. It is found in Thibet and 

 China, and is much used in India as a vehicle 

 for the solution of varnishes, &c. Boracic acid 

 was extracted from it, in 1702, by Homberg, and 



