302 ANNUAL OF SCIENTIFIC DISCOVERY. 



sumccl at a later period in the formation of gypsum. Ho supposes that 

 before gypsum was formed, there existed the easily soluble hyposulphite 

 of lime, and that it passed into gypsum by oxydation. For such a phe- 

 nomenon Fuchs offers two explanations, both of which accord whh chem- 

 ical principles, and one of which at the same time, accounts for the presence 

 of free sulphur in the gypsum beds. Either the hyposulphite of lime might 

 be converted into gypsum by immediate oxydation, and the free sulphuric 

 acid thereby formed also yield gypsum, by contact with neighboring car- 

 bonate of lime ; or the hyposulphite of lime might be resolved into sulphur 

 and sulphite of lime, and the latter pass into gypsum by absorption of 



oxygen. 



Instead of the theory of upheaval, Fuchs proposes a theory of collapse, 

 since by the crystallization of the amorphous masses they would assume 

 a smaller space, and thereby cavities and breaches must be formed, which 

 would result in dislocations, and the falling doAvn of large bodies of rock. 

 The half solid mass which was not crystallized might then penetrate the 

 rifts of the neighboring rock, thus giving origin to veins and dykes. In 

 these revolutions however Fuchs also admits certain upheavals. 



The views of Fuchs have found many objectors. Among others Bcrze- 

 lius controverted them and sought to weaken his chief argument against 

 the assumption that the earth was originally in a state of fusion, namely, 

 that in such case all lime must exist now as silicate and none as carbonate, 

 because at a high temperature silica expels carbonic acid from its combina- 

 tions, by asserting that the density of the vast quantity of aqueous vapor 

 in the atmosphere at that time would have been sufficient to balance the 

 tension of carbonic acid, so that it could remain in combination with lime 

 even in presence of silica. To this Fuchs replied, that at the fusing point 

 of silica, a temperature far higher than that of melted platinum, the tension 

 of carbonic acid must be so exalted that the pressure of the atmosphere 

 could not have prevented its escape, especially since the tendency of silica 

 to combine with lime must have facilitated this separation. 



OBSERVATIONS OX EOCK-SALT. 



We know that when we melt salt it crystallizes on cooling in different 

 forms, generally in cubes ; these crystals are more or less confused, opaque, 

 and always colored ; when common salt or crude rock salt is used, the 

 results arc different ; if salt sensibly pure is calcined and maintained in 

 a tranquil state of fusion, and cooled gently, it forms crystals sometimes 

 of a considerable size, and perfectly transparent. 



Out of the air we can melt rock-salt such as is found in nature, without 

 decolorizing it, that is to say, showing different tints of a grayish, red, 

 or brown color ; but if the calcination is made in the air, and, as in the 

 preceding case, the fusion is tranquil and the cooling slow, the salt is 

 completely decolorized, the earthy matters are deposited at the bottom 

 of the crucible, the chloride of magnesium decomposes itself spontaneously, 

 and in contact with the moist atmosphere the coloring matters are destroyed 



