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CHAPTER 4. 
Magnesia in the Limestone. 
Witn regard to Magnesia, the Limestone of Ply- 
mouth, generally speaking, contains this substance ; 
but in an extremely variable quantity. Although 
not professing myself a chymist, or pretending to 
great accuracy, yet I have been enabled to: submit 
certain portions of the rock to the test; so as to 
ascertain the fact, and to produce the following re- 
sults. From one hundred grains of the pure and 
very transparent crystal, I obtaimed a very small pro- 
portion of Magnesia ;—and, from the common grey 
Limestone, the produce of one hundred grains was 
rather more, amounting to about six or seven grains. 
