Magnesia Light

Alagnesium Oxide. Magnesia [1309-48 ] MgO, is available in a very bulky white powder known as light magnesium oxide, or a relatively dense white powder known as heavy magnesium oxide. It absorbs moisture and carbon dioxide when exposed to air. It is practically insoluble in water, insoluble in alcohol, and soluble in dilute acids (see Magnesium compounds). 

By shaking bromine water with finely divided magnesia, C. Lowig obtained a yellow liquid which at first behaved like an alkali towards litmus, but a more protracted action removed the colour, and when treated with weak acids gave off bromine. It is therefore supposed to be a soln. of magnesium hypobromite. A. J. Balard found that the soln. is decomposed by exposure to light, heat, or by evaporation in vacuo, and with an excess of bromine is converted into magnesium bromide and bromate. 

Not only was elective affinity inadequate as a means of comparing the affinities of different substances it also led to critical and pervasive errors in chemical analysis by compromising the purity of chemical substances obtained in this manner. In other words, the supposition of complete displacement reactions encouraged the use of impure substances as pure ones in chemical analysis, which seriously compromised the accuracy of chemical analysis. Chemists were deceived, for example, in believing that they could obtain pure magnesia from displacement reactions. Berthollet s pointed attack on the notion of elective affinity is understandable in light of the fact that it caused a serious problem for the validity of basic chemical analysis. His attack was quite successful in undermining chemists naive confidence in the absolute order of chemical affinities obtained from displacement reactions and in the analytic purity of the substances thus obtained. He discredited affinity tables as mere memorandums of barren facts ... 

The metal burns in air with a bright white light, to form magnesium oxide, MgO, the old name of which is magnesia ... 

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