Journal of the Chemical Society (Resumed)
Physical C hernis try. On the In$ue.izce which the Calcimxtion of some Metallic Oz(:cles cnwcisrr o n the Heat diseiqagecl in theiy Reactions. By A. DITTE.* As a preliminary to the investigation of the influence which the physical state of an oxide has upon the heat disengaged in chemical reactions, the density of magnesia in the bulky form was determined. The magnesia was prepared by calcining magnesium nitrate in an iron vessel containing boiling mercury. The product was a fine white powder,
... fine white powder, unctuous, and very bulky. A quantit,y of this substance was jntroduced into a tared specific gravity flask of about 25 C.C. capacity, and the weight ascertained. The flask was then put under the receiver of an air pump, through the neck of which a pipette with stop-cocks was secured, filled with turpentine specially prepared. A vacuum having been maiiitained for several hours, the stop-cocks of the pipette were gently opened, and the turpentine was allowed to descend into the flask below. After some time the flask was placed on a sand-bath, and slowly heated until the turpentine began to boil, after which it was closed with its stopper and allowed to cool under a bell-jar. By allowing it afterwards to remain in melting ice for an hour, the density at 0" was obtained, and by then subjecting it to thc heat of boiling water, the density was again ascertained. From these data, and the known density of the turpentine at 0" and at loo", the coefficient of expansion, a, between tliesc the two temperature8 was calculated by the formi&-- The vacuum was then renewed. This mcthod was found applicable to the othcr oxides to be considered in the sequel. Magnesia is amorphous, whatever the temperature of calcination has been. Four modifications have come under the author's obscrvnt)ion, differing in density, in expansibility, and in heat of combination. The higher the temperature of calcination, the less the expansibility, whereas the density increases, and the quantity of heat disengaged in combination with sulphuric acid also increases-a fact opposed to the ordinarily received opinion, that the heat evolved by a body diminishes * C'ompt. rend., lxxiii, 111 j 191-195, and 270.