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A. Solubility <>t' calcite and aragonite in pure water. 



In all following' experiments were used : for calcite fragments of 



the calcite of Iceland and for aragonite crystals of Bilin in Bohemia. 



By pulverizing and sieving a powder was obtained the grains of 



which were all smaller than 2 nun. and larger than 1 mm. in order 



to equalize the circumstances. 



To compare the solubility of the two minerals in pure water, a 

 quantity of* 1 or 2 grains of this powder was exposed during a week 

 to 200 cm', of newly distilled water and afterwards the quantity 

 was again weighed accurately. 



I obtained the result that the same quantity of pure water in the 

 same time dissolved : 



from the calcite powder: 



4,8 milligrams 

 5,0 

 5,1 

 and from the aragonite powder: 



2,8 milligrams 



3,0 



3,2 



On these numbers a remark is to be made, to which prof. Dr 

 Gr. A. F. Molengraaff drew my attention. The grains of calcite will 

 have the form of the cleavage rhomboeder and will moreover show 

 small internal fissures. This has the consequence that the attackable 

 surface offered by the calcite powder is much larger than that of 

 the aragonite powder. 



For this reason I experimented another time with the fines! powder 

 of the two minerals which had passed a silk sieve of b'4 openings 

 on the m.M.'-. I acted during the same time with the same quantities. 



which Prof. Dr. S. Hoogewerff drew my attention. According to the law that of 

 two forms the least soluble is the most durable, the author finds in different ways 

 that under the normal circumstances of pressure and temperature calcite is more 

 durable than aragonite. Formerly it had already been shown by experiments of 

 Kohlrausgh and Rose that at the temperatures between 2° and 34° G. calcite is 

 somewhat less dissoluble in water than aragonite. The author finds the same fact 

 at the temperatures 25°, 50 ^ and 59° G. By means of the electric properties the 

 difference in solubility in water containing carbonic acid is examined at the tem- 

 peratures of 8 •, '25°, 41° and 48° G. At 49° G. aragonite is still 11% more 

 soluble than calcite, though the difference becomes smaller at rising temperature. 

 The relations of solubility found in this essay agree satisfactorily with the results 

 found by me by direct weighing. 



