ON THE PREPARATION OP PHOSPHATE OF SODA. 145 
ART. XL.— ON THE PREPARATION OF PHOSPHATE OF SODA. 
BY THE EDITOR OF " THE DUBLIN HOSPITAL GAZETTE." 
Phosphate of soda is prepared, according to the direc- 
tions of the "Dublin Pharmacopoeia," by forming a soluble 
super-phosphate of lime by the action of sulphuric acid on 
bones burnt to whiteness, and decomposing this super-phos- 
phate by means of carbonate of soda ; the excess of phos- 
phoric acid unites with the soda forming phosphate of soda 
which dissolves, while insoluble phosphate of lime is thrown 
down, and carbonic acid is given off with effervescence. 
Now, I have observed, that when the solutions of super- 
phosphate of lime and carbonate of soda are mixed cold, 
and the mixture filtered for the purpose of separating the 
precipitated phosphate of lime, the liquid, when poured in- 
to a Wedgewood dish, and placed in a sand-bath, becomes 
turbid as it grows warm, and the effervescence at the same 
time becomes renewed ; these phenomena continue until 
the solution attains a boiling temperature, so that it is 
necessary to refilter before crystallisation is permitted to take 
place. 
The explanation of these facts is as follows: — when the 
excess of phosphoric acid decomposes the carbonate of soda, 
the carbonic acid liberated does not all escape, but some of 
it unites with a moiety of the lime, forming bi-carbonate of 
lime, liberating phosphoric acid which combines with the 
undecomposed phosphate of lime regenerating the super- 
salt. Now, both the bi-carbonate of lime, and super-phos- 
phate of lime are soluble, so that when the. solutions are 
mixed in the cold, the whole of the carbonic acid does not 
escape, nor does the whole of the phosphate of lime preci- 
pitate. A precisely similar reaction takes place when a 
stream of carbonic acid gas is passed through water holding 
phosphate of lime in suspension ; the carbonic acid gradually 
