416 Dr. Thomas Thomson on the 



fore subjected it to analysis, and found it a compound of 9 

 atoms carbonate of strontian, and 2 atoms carbonate of 

 lime. 



Tbe colour of this mineral is snow white ; the structure 

 obscurely foliated, but imperfect cleavages may be obtained 

 in the direction of a right oblique prism. My attempts to 

 measure the angles of this prism, even with a common go- 

 niometer, were frustrated by the unevenness of the cleav- 

 age faces. I found the great angle of the prism to be 113°, 

 and the small one 63°. It is obvious that no reliance can 

 be placed on these measurements, as the two together, in- 

 stead of 180°, make only 176°. 



Fracture in the direction of the cleavage planes flat and 

 smooth ; but the mineral in general had a scaly appearance, 

 not unlike some varieties of gypsum. 



Translucent on the edges. 



Very easily reduced to powder. 



Hardness 2-75. Specific gravity 2*9463. 



100 grains of the mineral were dissolved with efferves- 

 cence in nitric acid, except a residue of 3*79 grains, con- 

 sisting of particles of zeolite, quite white, and easily crushed 

 between the fingers. The solution, mixed with ammonia, 

 let fall one grain of peroxide of iron, with a trace of alu- 

 mina. The solution, freed by heat from nitrate of ammo- 

 nia, weighed 139 grains. 



I now examined the crystallized matter, and found it to 

 be a mixture of nitrate of strontian and nitrate of lime, and 

 nothing else. The nitrate of lime was separated by digest- 

 ing the salt in absolute alcohol. Hence, the composition 

 was easily deduced. But it may be determined with equal 

 accuracy from the following data : — 



The carbonates of strontian and lime weighed 95'21 grs. 



The nitrates of ditto 139 grs. 



The atom of strontian weighs 6*5. Let the number of 

 atoms in 100 grains of the mineral be x. 



The atom of lime is 3-5. Let the number of atoms pre- 

 sent be y. 



The atom of nit 'ic acid = 6-75. Number of atoms in 

 the nitrates = 6-75 (x + y). 



The atom of carbonic acid = 2*75. Number of atoms in 

 the carbonates = 2*75 (x + y). 



