liv GENERAL SUMMARY OF SCIENTIFIC AND 



lias studied the thermal changes produced when acids or al- 

 kalies are dissolved in water, with the expectation of solving 

 the question of hydratation. lie has also given a descrip- 

 tion in a subsequent memoir of the various pieces of appara- 

 tus which he has employed in his calorimetrical experiments. 

 These are, a helicoidal agitator for mixing the water of the 

 calorimeter, an ecraseur for crushing salts and other solids in 

 liquids, a distilling apparatus, with worm and receiver, for 

 effecting reactions out of contact with water, an apparatus 

 for measuring the heat of solution at elevated temperatures, 

 a closed apparatus for the reaction of nitrogen dioxide on 

 oxygen, and an apparatus for decomposing ammonium nitrite 

 by heat. 



Thomsen has made another series of investigations in ther- 

 mo-chemistry, in which the heat of combination of manga- 

 nese, zinc, cadmium, and iron has been determined. Com- 

 bining these results with previous ones, it appears that for 

 the nine metals which decompose hydrochloric acid with evo- 

 lution of hydrogen, the heat of combination for every mole- 

 cule of hydrogen thus evolved is, for lithium, 125,860 calories; 

 for potassium, 123,700 ; for sodium, 114,380; for magnesium, 

 108,290; for aluminum, 79,880; for manganese, 49,360; for 

 zinc, 34,200; for iron, 21,310; and for cadmium, 17,610 ca- 

 lories. 



Boisbaudran has shown that a remarkable inequality of 

 action is exerted by a given supersaturated solution upon 

 different isomorphous bodies. A perfectly regular ciwstal 

 of potassio-chrome alum, placed in a slightly supersaturated 

 solution of ammonio-alumina alum which had been rendered 

 basic, so as to crystallize in cubes was soon covered with a 

 white octohedric envelope showing cubic facets. After a 

 longer time the cubic facets had increased considerably, but 

 the distances between opposite solid angles of the octohedron 

 remained unaltered. Hence the author concludes that the 

 solution must have been supersaturated relatively to the oc- 

 tohedral faces of the ammonio-alumina alum, but not rela- 

 tively to the cubic faces of the same alum. In general it ap- 

 pears that in the phenomena of solution and crystallization, 

 the molecular volume, the density, the relative arrangement 

 of the similar or dissimilar atoms in the molecule, and all 

 other causes of dissimilarity, possess their special influences. 



