of Cale Spar and Arragon ile. 473 



containing any such portion of strontla. I purposely mixed 

 a small quantity of a solution of chloride of strontia with a 

 solution of chloride of lime, but by precipitation at the 

 common temperature with carbonate of ammonia only crystals 

 of calc spar were perceivable. 



The form of arragonite is also found in witherite, stron- 

 tianite, and white lead ore, or the neutral carbonates of 

 barytes and strontia, and carbonate of lead : however, I have 

 not succeeded in producing this substance in the second rhom- 

 bohedral form as in the carbonate of lime by the above-men- 

 tioned method. 



If carbonate of barytes be dissolved in hydrochloric acid, 

 and the solution precipitated with carbonate of ammonia, 

 we obtain (the solution may have been hot or cold,) a preci- 

 pitate, which examined under the microscope consists of very 

 distinct crystals similar to those of arragonite. 



If we treat carbonate of strontia in the same manner, we 

 recognise under the microscope, from the hot solution very 

 distinct crystals quite similar to those of arragonite ; the pre- 

 cipitate from the/ cold solution as aggregated globules, which 

 do not allow of our distinguishing any fixed form. 



With the carbonate of lead the case was the reverse ; here 

 the precipitate from a cold solution produced crystals similar 

 to those of arragonite (which however were much smaller and 

 less distinct than in the carbonates of barytes and strontia); 

 the precipitate from a hot solution gave an opake indistinct 

 mass. It is however probable that we also obtain, from the 

 cold solution of the chloride of strontia and from the hot so- 

 lution of chloride of lead, crystals which are determinable, if 

 we find out the favourable circumstances under which the 

 crystals are formed, which however from this would probably 

 always have the form of arragonite. This also explains why 

 it is that a small mixture of carbonate of strontia frequently 

 occurs in arragonite, but never in calc spar, (at least has not 

 hitherto been found in it,) not even when calc spar and stron- 

 tianite occur grown together. Even thus we do not find in 

 calc spar carbonate of barytes, but this forms with calc spar a 

 double salt, baryto-calcite, which is evidently a combination 

 of 1 atom of calc spar with 1 atom of witherite. Carbonate 

 of lead alone is sometimes found in small quantities in calc 

 spar : such a combination Johnston has described under the 

 name of plumbo-calcite. 



If I did not succeed in producing in the form of calc spar 

 the latter carbonates which occur only in the form of ar- 

 ragonite, I was so fortunate as to obtain a carbonate in the 

 form of arragonite which occurs only in the form of calc spar 



