26 
freshly precipitated, but on standing for about half an hour 
without heating, it became crystalline in appearance. The 
dried precipitate under the microscope was distinctly crys- 
talline, being apparently composed of minute rhombohedra. 
In subsequent experiments we found the microscopic 
appearance to vary, sometimes rhombohedra mixed with 
minute prisms making their appearance. 
On analysis we found that the crystalline powders (they 
were only just perceptibly crystalline to the naked eye) con- 
tained according to two experiments : — 
CaC0 3 Na 2 C0 3 
( 5 ) 
97-65% ... 97-90% 2-46% 
It would seem probable from this that the major reaction, 
so to say, is that converting sodium carbonate into hydrate, 
calcium hydrate passing into pro rata carbonate, but a minor 
reaction also occurs by which a small quantity of a double 
carbonate is formed. It is all the more certain that such a 
compound actually is formed from the fact that the precipi- 
tates obtained as j nst mentioned (and this experiment has 
been repeated many times) were in every case distinctly 
crystalline powders; we never detected the smallest amor- 
phous particle with the microscope. Now it is hard to 
imagine any difficulty in removing sodium carbonate by 
continued washing with boiling water in excess, from a 
powder consisting of distinct crystals of calcium carbonate. 
We can then best account for the presence of the alkali by 
considering it as having formed itself, a crystalline and 
insoluble compound with calcium carbonate, this double 
crystalline carbonate being mixed in small quantity with 
the superabundant calcium carbonate. 
Another experiment was now tried, to prove indirectly if 
