178 ESSAYS anp OBSERVATIONS | 
Repeat this wafhing with the cold water 
ten or twelve times, or even Oftner, if the 
magnefia be required perfectly pure for che- 
mical experiments. 
WHEN it is fufficiently wafhed, the wa- 
ter may be ftrained and fqueezed from it 
in a linen cloth; for very little of the —, 
nefia pafles through. 
THE alkaliin the mixture uniting with 
the acid, feparates it from the magnefia; 
which, not being of itfelf foluble in water, 
muft confequently appear immediately 
undera folid form. But the powder which 
thus appears is not intirely magnefia; part 
of it is the neutral falt formed from the 
union of the acid and alkali. This neu- 
tral falt.is found, upon examination, to a- 
gree in all refpects with vitriolated tartar, 
and requires a large quantity of hot wa- 
ter to diffolve it. As much of it is there- 
fore diffolved as the water can take up; _ 
the reft is difperfed through the mixture in 
the form of a powder. Hence the necef- 
fity of wafhing the magnefia with fo much 
trouble; for the firft affufion of hot water 
is intended to diffolve the whole of the — 
falt, 
