CARBONATES

Saline compounds in definite proportions, of carbonic acid, with alkalis, earths, and the ordinary metallic oxides. The carbonates principally used in the arts and manufactures are those of ammonia , copper , iron , lead , lime , magnesia , potash , soda . Native carbonate of copper is the beautiful green mineral called Malachite . Carbonates are easily analyzed by estimating either by weight or measure the quantity of carbonic acid which they evolve under the decomposing action of somewhat dilute sulphuric, nitric, or muriatic acid; for as they are all compounds of acid, and base in equivalent proportions, the quantity of acid will indicate the quantity of base. Thus, as pure limestone consists of 56 of lime and 44 of acid, in 100 parts, if upon examining a sample of limestone we find it to give out only 22 per cent. of carbonic acid gas, during its slow solution in muriatic acid, we are sure that there are only 28 parts of lime present. I have described, in the Annals of Philosophy, for October, 1817, a simple form of apparatus for analyzing the carbonates with equal readine and precision. The simple rule by measure to which I was led, may be thus stated: From the bulk of evolved gas, expre ed in cubic inches and tenths, deduct 1 ⁄ 20 , the remainder will expre the proportion of real limestone present in the grains employed. Pure magnesian limestone yields very nearly a cubic inch of the gas for every grain in weight.