PHYSICAL anp LITERARY. 179 
falt, and the fubfequent additions of cold 
water to wafh away this folution. 
THEcaution given of boiling the mixture 
is not unneceffary ; if it be neglected, the 
whole of the magnefia is not accurately {e- 
parated at once; and, by allowing it to reft 
for fome time, that powder concretes into 
minute grains, which, when viewed with 
the microfcope, appear to be affemblages 
of needles diverging from a point. This 
happens more efpecially. when the folution 
of the Epfom-falt and of the alkali are di- 
luted with too much water before they are 
mixed together. Thus,if a dram of Epfom 
“falt and of falt of tartar be diffolved each 
in four ounces of water,and be mixed,and . 
then allowed to reft three or four days, the 
whole of the magnefa will be formed into 
thefe grains. Or, if we filtrate the mixture 
foon after it is made, and heat the clear 
liquor which pafles through, it will be- 
_ come turbid, and depofite a magnefia. 
_ Thad the curiofity to fatisfy myfelf of 
pete purgative power of magnefia, and of 
“Hoffman's opinion concerning it, by the 
following eafy experiment. I made a neu- 
Oa. | tral 
