262 Miscellaneous Observations, chiefly Chemical. 



crystals, and not distinctly in granules. The obvious differ- 

 ence of circumstances in the two instances is, that, in the 

 first instance, the salt was precipitated from a solution con- 

 taining some vegetable matter derived from the corn ; and 

 that, in the latter, it was without, and I may say, unimpeded, 

 by that matter. In the mixed " fusible calculus," as it has 

 been called, consisting of a mixture of phosphate of lime and 

 of the ammoniaco-magnesian phosphate, we often see an 

 earthy chalky texture, the stone being formed in part, or 

 altogether, of loosely adhering granules. Reasoning from 

 analogy, may not this peculiarity be owing to a cause such 

 as has been supposed to have had an effect in the instance 

 above described, viz., being deposited from a fluid containing 

 an organized matter in solution, and some of which enters into 

 the composition of the calculus % And may not the same cir- 

 cumstance be connected with the fact, that the urinary calculi 

 generally are little crystalline ? 



10. Ammonia, as it is w^ell known, occasions a precipitate 

 of magnesia when added to a solution of sulphate of magnesia. 

 But, however much in excess it be added, it does not preci- 

 pitate the whole of the magnesia ; a definite portion remains ; 

 a new salt is formed — a double salt, consisting of the whole of 

 the acid in union with the unprecipitated earth, and a portion 

 of alkali equivalent to the portion of earth thrown down. 

 That this is the case, may be inferred from the following re- 

 sults. The precipitate obtained by the addition of a solu- 

 tion of ammonia to one of sulphate of magnesia, after having 

 been well washed in a filter, yields no smell of the volatile 

 alkali when mixed with quicklime, nor, when dissolved by 

 means of nitric acid, any indication of sulphuric acid in union 

 with it by the test of nitrate of baryta, proving that this 

 precipitate is pure magnesia. If the solution from whence 

 a portion of magnesia has been thrown down by the volatile 

 alkali be evaporated, a salt in a crystalline form, deliques- 

 cent in a moist atmosphere, will be obtained, which appears 

 to have the same properties as the double salt of sulphate of 

 ammonia and sulphate of magnesia. "When carefully heated, 

 it first enters into the watery fusion ; and when the greater 

 part of the water is expelled, on slowly raising the heat. 



