264 M. Beudant on the Connexion between [April, 



It appears, from this definition, that the results of chemical 

 analyses, and those derived from crystallography, are both jointly 

 regarded. But in its application, it will be seen that the author 

 assigns the greatest degree of importance to crystallography ; not 

 from any particular predilection for a science which he, as it were, 

 created, but in consequence of a strict examination of each 

 species, and into the degrees of exactitude and constancy, 

 observable in the results both of chemical analysis and of crystal- 

 lization. This preference given to crystallographical character* 

 has led M. Haiiy to separate bodies which chemistry had placed 

 together, and to unite others which chemistry had separated. 

 The same elements, and frequently in nearly similar proportions, 

 being found connected with incompatible crystallization ; and 

 on the other hand, elements dissimilar in number and proportion 

 being discovered in uniformly crystallized bodies. 



These facts have been shown by M. Haiiy, in his Tableau 

 Comparatif ; and he hence concludes, that, to determine the true 

 constituent elements of compound bodies, it is required to sepa- 

 rate the accidental mixtures from the result of the analysis. 

 But as he does not discover, in the present state of the science 

 of chemistry, a method of distinguishing the essential elements 

 from the accidental mixturea r hexonceives that the crystallogra- 

 phical character may be the most constantly and certainly relied 

 upon for the classification of such bodies as chemistry would 

 leave undecided. 



These conclusions, which have received the concurrent sanc- 

 tion of many men of science, have nevertheless not been adopted 

 generally; and particular analyses are frequently adduced to 

 establish new species, in opposition to their crystallographical 

 character. 



Chemists agree generally, with M. Haiiy, that accidental 

 mixtures enter into the composition of minerals, and that these 

 must be separated before the true component parts can be 

 known ; but,, they observe, that in many cases it would be neces- 

 sary to separate one half, or two thirds, of the compound, ia order 

 to produce an accordance between the chemical and crystallo- 

 graphical characters, and they have considered this proportion 

 too great to be the result of accident. It is to elucidate 

 this circumstance that the following experiments were under- 

 taken. 



It is now generally known that the same compound constantly 

 gives the same crystals ; but the inverse of this proposition, 

 which would infer similarity of composition from similarity of 

 form, is true only in theory, or when the compound is perfectly 

 pure. In natural compounds, as well as in those producedin the 

 laboratory, it is frequently contradicted by our experience. 



Mineralogists explain these differences of composition by sjnx- 

 poBiug the addition of accidental mixtures to the constituent 

 ^kments of bodies, although, from our ignorance of the elements 



