358 Samuel Lewis Penfield. 



cate the probable existence of another member of the series 

 and to predict its composition and properties, a forecast whose 

 correctness has since been established by Sjogren in the dis- 

 covery of prolectite. 



The idea of the isomorphism between hydroxyl and fluorine 

 was suggested in the first Branch ville paper by Brush and 

 Dana from Penfield's analysis of triploidite. At first it was 

 not accepted by prominent chemists and mineralogists, but 

 Penfield by steady work in his laboratory again and again 

 demonstrated its validity and importance, until now it has 

 gained general acceptance and it has become recognized that 

 the existence of these isomorphous radicals not only explains 

 the structure of many minerals, but that their presence is 

 of the greatest importance in understanding the mode of forma- 

 tion, especially in magmatic processes. 



Another contribution of the first order, in the field of 

 chemical crystallography, was his announcement of the mass 

 action of complicated inorganic acids in determining crystal 

 form. Thus while the bases in combination with such acids 

 may be of the most diverse kinds, the system of crystalliza- 

 tion is not affected. This was brought out in his important 

 paper with Foote on the chemical composition of tourmaline, 

 but has since been shown to be of wide application. 



As an analytical chemist Penfield must be ranked as one of 

 the great masters of this art. He had a broad and compre- 

 hensive grasp of its principles, was very fertile in their appli- 

 cation, suggestive in combinations and in details and joined 

 to this a technical skill and dexterity in manipulation that. was 

 really marvelous. In consequence of this the ease and speed 

 with which he turned out complicated analyses of remarkable 

 accuracy have always been a source of admiration among his 

 friends and fellow- workers. His analysis of the rare mineral 

 connellite and derivation of its formula was performed upon 

 less than a tenth of a gram of material. Many similar feats 

 of his skill might be cited. He rarely took up any new 

 analytical method that he did not suggest excellent improve- 

 ments in it, and he devised new methods, many of which are 

 now in general use ; his mineralogical papers in fact are full 

 of contributions to analytical chemistry and he published 

 several useful papers directly upon analytical methods. 



