ON PRECIPITATED CARBONATE OF LIME. 163 
now cohere when dry, both to each other and the contain- 
ing vessel, as is usual with fine powders. 
This difference is due to the dimorphous character of 
carbonate of lime, and the influence of temperature in bring- 
ing out and rendering this condition manifest. At low tem- 
peratures the ordinary form of crystal, viz., that of rhomb 
spar (the regular rhombohedron) is produced; but at high 
temperatures, the more rare configuration of arragonite, 
(six-sided prism,) is the result. The former occurring in 
nature, always of manifest size ; the latter generally in mi- 
nute crystals. 
From the above remarks it must be evident, that the 
Dublin formula should afford a tolerably good pharma- 
ceutical preparation, although it does not combine all the 
circumstances necessary for the best result. In this formula 
a strong solution of chloride of calcium (Ca CI 2 parts, to aq. 
7 parts.) is precipitated by a strong solution of carbonate of 
soda, (NaOC0 2 3 parts, to aq. 12 parts,) but no reference 
is made to temperature, hence ordinary temperatures are to 
be understood ; and the result is, that although the particles 
of the powder are very small, yet some degree of grit may 
be detected by the tongue. The article imported into this 
city, may be presumed to be formed by this process, as it 
cannot be distinguished by any character from that prepared 
according to these directions. To produce the best prepara- 
tion it is only necessary to modify this process by using boil- 
ing solutions, to produce a precipitate as minutely divided 
as may be desired, and in which no grit can be detected. 
