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it is procured by chemists, it appears in the form 
of a white impalpable powder. It is not soluble 
in the common acids, but dissolves by heat in 
fixed alkaline lixivia. It is an incombustible sub- 
stance, for it is saturated with oxygene. I have 
proved it to be a compound of oxygene, and the 
peculiar combustible body which I have named 
silicum ; and from the experiments of Berzelius, 
it is probable that it contains nearly equal weights 
of these two elements. 
2. The sensible properties of lime are well 
known. It exists in soils usually united to car- 
bonic acid ; which is easily disengaged from it by 
the attraction of the common acids. It is some- 
times found combined with the phosphoric and 
sulphuric acids. Its chemical properties and agen- 
cies in its pure state will be described in the 
Lecture on manures obtained from the mineral 
kingdom. It is soluble in nitric and muriatic 
acids, and forms a substance with sulphuric acid 
difficult of solution, called gypsum. It is not 
soluble in alkaline solutions. It consists of one 
proportion 40 of the peculiar metallic substance, 
which I have named calcium ; and one proportion 
15 of oxygene. 
3. Alumina exists in a pure and crystallized 
state in the white sapphire, and united to a little 
oxide of iron and silica in the other oriental gems. 
In the state in which it is procured by chemists, 
it appears as a white powder, soluble in acids and 
fixed alkaline liquors. From my experiments, it 
appears that alumina consists of one proportion 
33 of aluminum, and one 15 of oxygene. 
