274 PROGRESS OF SCIENCE IN THE CENTURY. 



predating the study of the chemical properties, em- 

 phasised the value of crystallography, and referred 

 the numerous crystalline forms to a few primary 

 types. 



There was for a time a tendency among mineral- 

 ogists, as among physiologists, to refuse the chemists* 

 offer of a helping hand, but sounder views gradually 

 prevailed. Berzelius (quoted by E. von Meyer) com- 

 pares the mineralogist who refuses the aid of chem- 

 istry to a man who objects to use a light in the 

 dark, on the ground that he would thereby see more 

 than he requires to. The introduction of the blow- 

 pipe by Cronstedt was an event of much importance, 

 and led on to the early chemical systems of Bergmann 

 and others. But the modern study of mineralogical 

 chemistry must date from the work of Berzelius, 

 who in his Chemical System brought minerals into 

 line with other inorganic compounds. The general 

 tendency of subsequent systems of classification 

 seems to have been to emphasise chemical composi- 

 tion, and it is interesting to notice the suggestions of 

 Wurtz and others as to the collation of various min- 

 erals with organic compounds, e.g., poly-silicic acids 

 with poly-ethylene alcohols. 



Isomorphism. — Another great event in the history 

 of mineralogy was Mitscherlich's discovery of isomor- 

 phism. IN". Fuchs had previously observed that cer- 

 tain substances can replace each other in minerals; 

 Mitscherlich showed tiiat the same material might 

 have two, three, or more crystalline forms. This set 

 aside the exaggerated conclusion of Haiiy that 

 difference in crystalline form necessarily implies 

 difference in chemical composition. 



While Mitscherlich may be said to have proved 

 irrefutably the connection between chemical com- 



