DISAPPEARANCE OP CARBONATE OF LIME IN SOILS. 76 



often be found to consist more of carbonate of lime, than of mag- 

 nesia. The following are examples of such products : 



One thousand grains of tide-marsh soil (page 63, No. 4), acted 

 on by muriatic acid in the pneumatic apparatus, gave out no car- 

 bonic acid gas, and therefore could have contained no carbonate of 

 lime. The precipitate obtained from the same weighed sixteen 

 grains ; which being again acted on by sulphuric acid, evolved as 

 much gas as showed that three grains had become carbonate of 

 lime, in the previous part of the process. 



Two hundred grains of alluvial soil from Saratoga Springs (page 

 65, No. 18), containing no carbonate of lime, yielded a precipitate 

 of twelve grains, of which three was carbonate of lime and a 

 deposit from the alkaline solution weighing six grains, four of 

 which was carbonate of lime. 



Seven hundred grains of limestone soil from Bedford, Pennsyl- 

 vania (part of the specimen marked 14, page 64), contained about 

 two-thirds of a grain of carbonate lime and its precipitate of 

 twenty-eight grains, only yielded two grains : but the alkaline 

 solution deposited eleven grains of the carbonates of lime and 

 magnesia, of which . at least five was of the former, as there 

 remained seven and a half of solid matter, after the action of sul- 

 phuric acid.* 



[Eleven hundred and fifty grains of the rich alluvial earth depo- 

 sited by the Mississippi river, in Arkansas, yielded, in the pneu- 

 matic apparatus, 9 ounce measures of carbonic acid gas, and 

 of course could not have contained more than nineteen grains of 

 carbonate of lime, or, so far as the carbonate was of magnesia, 

 something less in proportion. But by adding carbonate of potash 

 to the acid solution, fifty-two grains were precipitated, all of which, 

 according to Davy, should have been carbonate of lime ] and from 

 the alkaline solution thus made, by standing and boiling, 20 J 

 grains more of solid matter was precipitated, which, according to 

 Davy, should have been carbonate of magnesia ; and making of 



* The measurement of the carbonic acid gas evolved was relied on to 

 show the whole amount of carbonates present and sulphuric acid was used 

 to distinguish between lime and magnesia, in the deposit from the alkaline 

 solution. If any alumina or magnesia had made part of the solid matter 

 exposed to diluted sulphuric acid, the combinations formed would have 

 been soluble salts, which would of course have remained dissolved and in- 

 visible in the fluid. Lime only, of the four chemical earths, forms with 

 sulphuric acid a substance but slightly soluble, and which therefore can be 

 mostly separated in a solid form. The whole of this substance (sulphate 

 of lime) cannot be obtained in this manner, as a part is always dissolved ; 

 but whatever is obtained, proves that at least two-thirds of that quantity 

 of carbonate of lime had been present ; as that quantity of lime which will 

 combine with enough carbonic acid to make 100 parts (by weight) of car- 

 bonate of lirae, will combine with so much more of sulphuric acid, as to form 

 about 150 parts of the sulphate of lime, or gypsum. 



