Report’ OF THE CHEMIST. 389 
LIME. 
The word lime is ordinarily used to designate a compound 
consisting, when pure, of calcium (71.5 per ct.) and oxygen 
(28.5 per ct.), which is known to chemists as calciwm owid 
(CaO). At one time it was supposed that calcium oxid (lime) 
was present in the different compounds of calcium, and so all 
calcium compounds were called lime compounds. This inac- 
curate use has continued, especially in commercial practice. 
Calcium oxid, in impure forms, is known under several com- 
mercial names, such as lime, quicklime, burntlime, stone-lime, 
lunp-lime, etc. The value of commercial lime depends, for 
many purposes, upon its freedom from impurities, that is, wpon 
the amount of calcium oxid it contains. . 
Commercial lime is prepared by heating at a sufficiently high 
temperature any form of carbonate of lime (calcium carbon- 
ate), the carbon dioxid (carbonic acid) being driven off as a 
gas and calcium oxid remaining as a solid residue. The ma- 
terials most commonly used as a source of commercial lime 
are limestone, oyster shells and shell-marl. It is evident that 
the purity of a lime (the percentage of calcium oxid present) 
depends upon (1) the purity of the original carbonate rock 
used, (2) the completeness of the burning, and (3) subsequent 
care in keeping dry. The impurities commonly found in com- 
mercial lime are compounds containing magnesium, silicon, 
iron, and aluminum. The three most common forms of com- 
mercial lime are: (1) Stone-lime, (2) magnesian stone-lime, 
and (38) oyster-shell lime. 
Stone-lime. This is the ordinary lump-lime commonly used 
by masons. It is prepared from limestone (calcium carbonate) 
of a good degree of purity and contains 90 to 98 per ct. of 
calcium oxid. 
Magnesian stone-lime. This is prepared from limestone that 
contains more or less magnesium carbonate, the proportions 
varying greatly in different varieties. Commercial lime pre- 
pared from such material contains 55 to 85 per ct. of calcium 
oxid and 10 to 40 per ct. of magnesium oxid. The presence of 
