^44 ^'2 the different Sorts ej Lime ufed in Agriculture. 



incumbent upon a calcareous IlratHm ; for in defcending a cave formed in this rock, 

 a diftinft vein of common lime-flone may be obferved wliich contains no magnel a. The 

 latter flratum is very full of fhells ; but though there is fome alfo in the magnefian rock, 

 yet they are very rare. In the following tables, containing the analyfis of various fpe- 

 timens, fome other places arc mentioned where this fubflancc is found, but of which I 

 received no further information. 



Although it was known that the magnefian marble and lime-ftone conffted ©f two 

 carAs, their proportion was attempted to be difcovercd by trying how much gypfum 

 and epfom fait could be obtained by means of vitriolic acid from a certain weight of 

 each fpecimcn. When the fuperfluous vitriolic acid had been evaporated by heat, tha 

 Kpfom fak was feparated from the Gypfum by water. The refult of thefe trials is cx- 

 preffcd in the following table. 



3 grs. of calcareous fpar and 1 gr. of calcined mag- "\ 



nefiagave ^ J 6<y u 



As the preceding method of eftimating the quantities of magnefia and calcareous 

 earth is liable to confiderable error, I afterwards examined them in the following man- 

 ner, which feems capable of great exaftnefs. Twenty-five grains of each fubflance 

 were diffolved by marine acid in a cup of platina, and after the folution was evaporated 

 to drynefs, it was made red hot for a few minutes. The mafs remaining in the cup 

 which confiRcd of muriated lime, and of the magnefia freed from the acid, was wafhed 

 out with water and poured into a phial . There was then added to it a known quantity 

 of diluted marine acid, fomewhat more than was fufficient to re-diffolve the magnefia, 

 and after the folution a certain weight of calcareous fpar, part of which would be dif. 

 folved by the fuperfluous acid. By the quantity of that remaining undiffolved it was 

 learnt how much acid was required to diffolve the magnefia. The iron and argillaceous 

 earth, contained in fome fpecimens, vicre precipitated by the fpar, and therefore could 

 not occafion any error. Thp calcareous fpar, however, diffolved more flowly where 

 there was argillaceous earth, as it became coated with it ; but this incrufiation was oc- 

 cafionally removed, and in all the experiments the fpar was left in the folution till it 

 fuffered no further diminution. For this purpofe it was neceffary to keep them flightly 

 warm for fome days, during which time the phials were generally clofed to prevent any 

 cfcape of the acid. The firfl experiment in the following table was made upon known 

 quantities of magnefia and calcareous sarth to try the accuracy of the procefs. For 



this 



