500 Dr Fyfe on tile Action of Water 
a red heat for some time, till the whole of the carbonic acid was 
expelled, having previously washed it, till the fluid which passed 
through the filter did not become turbid on the addition of ni- 
trate of baryta; shewing that there was not an excess either of 
the sulphate of the earth, or of the carbonate of the alkali. 
As the quantity of magnesia taken up by water is but small, 
I thought that the best method of throwing it down from its so- 
lution, would be by the addition of ammonia and phosphoric 
acid, so as to procure phosphate of magnesia and ammonia, which, 
after being subjected to a high temperature, gives out its alkali, 
and phosphate of magnesia is left, which is stated to contain, in 
a 100 parts, 40 of earth. 
Exp. 1. Water at the temperature of 60° was kept on 
magnesia for several hours, and the fluid was then filtered. 
To twelve ounces of this, (5760 grains,) carbonate of ammo- 
nia, and then phosphate of soda, were added, and the precipi- 
tate thrown down was washed, till the fluid which passed 
through was not altered by nitrate of baryta, indicating that the 
whole of the alkaline salts was removed. After exposure to a 
red heat, it weighed 2.8 grains. 
Exp. 2. Water Avas boiled on magnesia for about half an 
hour, and the solution was then filtered as quickly as possible, 
pouring but a small quantity on the filter, and keeping the re- 
mainder boiling during the filtration. From 5760 grains of 
this, after it had become cold, the magnesia was thrown down, 
as in the former experiment, and the precipitate was washed 
and treated in the same way, after which it weighed 0.4 of a 
grain. 
Phosphate of magnesia and ammonia, as has been already 
stated, contains, after being heated to redness, 40 of earth in 
100 parts. 2.8 of the precipitate, therefore, are equal to 1.12, 
which is the quantity of magnesia dissolved by 5760 of tem- 
perate water, 
and as 1.12 : 5760 : : 1 : 5142. 
Magnesia, then, is soluble in 5142 of water at a natural tem- 
perature. :• ’ *> 
Again, as 100 ; 40 : : 0.4 : 0.16, 
the proportion of magnesia held in- solution hy the boihng- water, 
and as 0 16 : 5760 : i 1 : 36000, ' - - • r . 
