PHYSICAL AND LITERARY. i6j 



folved as the water can take up ; the reft is 

 difperfed thro' the mixture in the form of a 

 powder. Hence the neceffity of wafhing the 

 magnejia with fo much trouble ; for the fir ft 

 afFufion of hot water is intended to diflblve 

 the whole of the fait, and the fubfequent ad- 

 ditions of cold water to wafti away this fo- 



•lution. 



The caution given of boiling the mixture is 

 not unneceflary J if it be negledted, the whole 

 of the magnefia is not accurately feparated at 

 once i and by allowing it to reft for fome 

 time, that powder concretes into minute 

 grains, which, when viewed with the mi- 

 crofcope, appear to be alTemblages of needles 

 diverging from a point. This happens more 

 efpecially when the folutions of the epfom- 

 falt and of the alkali are diluted with too 

 much water before they are mixed together. 

 Thus, if a dram of epfom-filt and of fait 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 magnejia 

 will be formed into thefe grains. Or if we 

 filtrate the mixture foon after it is made, and 

 heat the clear liquor which paffes thro' ; it 

 will become turbid, and depofite 2i magnejia. 



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