of a Spring on tJie Estate of' For del, S^-c. Ill 



lected very long and narrow, the absorption could not be such 

 as to account for the enormous deficiency. 



The remaining difficulty arises from the magnesia, not in re- 

 spect to the accuracy of the results obtained in Nos. 3. and 10., 

 but with regard to the calculations to be made from these re- 

 sults. In Dr Turner's work, page 684, it is stated that 100 

 parts of ammoniaco-phosphate contain 40 of magnesia ; and in 

 page 486, that 76 of the same salt contain 20 of magnesia. Which 

 of these statements is the correct one ? I have made my calcula- 

 tions according to the result of my own experiments on that salt, 

 which give 20 of magnesia from 55 of the precipitate. 



As connected with the water of this spring, it may be noticed 

 that there is a considerable efflorescence on the sides of the 

 quarry at Sunnybank, about half a mile to the westward, and 

 towards the rise of the strata. A solution of this efflorescence 

 gave with oxalate of ammonia no precipitate, but with nitrate of 

 barytes a most copious precipitate, the solution remaining scarce- 

 ly affecting nitrate of silver. With ammonia and phosphate of 

 soda, there was a most copious precipitate, and with tincture of 

 galls a considerable blackness. The solution of it deposited an 

 ochreous sediment on standing, and crystallized by evaporation 

 to the last particle in four sided prisms, terminated by short four 

 sided pyramids, the crystals often crossing one another. On ex- 

 posure to the air they became ochreous on the surface. With 

 ammonia and phosphate of soda, they yielded the same quan- 

 tity of ammoniaco-phosphate of magnesia, as an equal weight of 

 sulphate of magnesia did. They were, therefore, sulphate of 

 magnesia contaminated with a little iron. 



On the Cavities containing Fluids in RocTi-Salt. By William 

 NicoL, Esq. Lecturer on Natural Philosophy. Communi- 

 cated by the Author. 



Xhe rock-salt of England is in general of a reddish colour, 

 and more or less opaque ; but portions of it are often to be met 

 with, not only snow-white, but perfectly transparent. On in- 

 specting a specimen of the latter kind, which I lately received 



