CARBONATES. 389 



ate present ; a complete solution indicates a pure carbonate, proba- 

 bly of lime, or of lime and magnesia.* 



(e.) Expel the gas by a red heat, and compare the weight lost in 

 this trial and in the other experiment ; the loss may be a little great- 

 er on account of water. We must also try the residuum with an 

 acid to see whether it effervesces, and whether it contains mag- 

 nesia. f 



USES. As an antacid ; in chalk, as a crayon ; in marble and other 

 solid forms, as a building stone, valuable both for firmness and beau- 

 ty ; to afford lime by burning, and carbonic acid for the chemists and 

 manufacturers ; as a manure, both in the form of lime and of car- 

 bonate of lime the burning appears to be of no use, except to di- 

 minish weight and cohesion, so that it may be scattered in powder 

 on the land, where, if it be quick lime, it reabsorbs carbonic acid and 

 water, and becomes again carbonate of lime. 



CARBONATE OF BARYTA. 



1. DISCOVERY. 



(a.) By SCHEELE and BERGMAN, but Dr. WITHERING, J first 

 found the native mineral in 1783. 



2. PREPARATION. For demonstrations, the native carbonate of 

 baryta may be used, but for instruction, a number of processes may 

 be mentioned. 



(a.) By passing a current of carbonic acid gas through a solution 

 of pure baryta. 



(b.) By exposing the latter to the air, when a pellicle of carbonate 

 of baryta forms on the surface, and being removed, another suc- 

 ceeds, and so on, till the baryta is all precipitated. 



!c.) By mixing watery solutions of carbonic acid and baryta, 

 d.) By decomposing, by fire, the sulphate of baryta, 1 part ; by 

 the carbonate of a fixed alkali, 2 or 3 parts. 



(e.) By any alkaline carbonate, added to the nitrate or muriate of 

 baryta. 



(/.) By blowing air from the lungs through barytic water. 



lime stone, or 1 1-2 grains of lime for every grain the marl loses by the experiment 

 of expelling the air. Vinegar is not sufficiently strong, and it froths and becomes 

 clammy, and remains for several days without permitting all the gas to escape. 

 mack's Lect. Vol. II, p. 120. 



* The residuum, if any, should he dried, and weighed, and this may correct the 

 former conclusion. 



t If magnesia be present, it will be detected by sulphuric acid, which will form 

 a bitter soluble and crystallizable sulphate of magnesia, or Epsom salt. Such a marl or 

 limestone would be injurious, if applied in agriculture, in quantities as large as 

 when a pure calcareous earth is employed ; much less of it answers the purpose. 

 Nicholson's Jour. 4to. Vol. Ill, p. 440, Phil. Trans. 1799, part II, p. 305, and Bake- 

 well's Geology. 



t Called after him, Witherite. 



