348 Penfield — Chemical Composition of Turquois. 



Taking copper as a basis, the ratios of P : Cu : H in the resi- 

 dues are as follows : 







I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



Residues, 



) F 



1-20 



0-82 



1-15 



0-99 



0-78 



0-93 



0-09 



copper 



[Cn 



1-00 



1-00 



1-00 



1-00 



1-00 



1-00 



1-00 



as unity. 



)H 



3-65 



1-63 



2-09 



3-72 



4-56 



3-19 



0-90 



It is to be taken into consideration that it is a very severe 

 test of a formula to throw all of the errors resulting from pos- 

 sible imparities in the materials and inaccuracies of the analyses 

 upon a single constituent, in the case in hand on the supposed 

 copper salt ; but still the ratios of P : Cu : H are so variable 

 that it cannot be considered that turquois is a mixture of an 

 aluminium salt, Al 2 HP0 4 (OH) 4 , and a hyd rated copper phos- 

 phate having the definite composition 2CuO. P 2 5 . 4H 2 as sug- 

 gested by Clarke. A compound having the composition 

 2CnO. P 2 5 . 4H 2 demands a ratio of P : Cu : H = 1 : 1 : 4. 



An important factor to be taken into consideration is that 

 the hydrogen in turquois is to be regarded as representing 

 hydroxy 1 and not water of crystallization, for water is not 

 expelled from the mineral at a low temperature ; hence 

 hydroxyl radicals may be considered as playing a part in the 

 chemical composition of the mineral. Considering copper as 

 an essential constituent of turquois and not as an impurity, two 

 theories naturally suggest themselves : one, that the bivalent 

 copper is isomorphous with, and replaces the bivalent alu- 

 minium-hydroxide radical [A^QH)]" ; the other, that the 

 univalent copper-hydroxide radical [Cu(OH)] / is isomorphous 

 with the univalent aluminium-hydroxide radical [Al(OH) a ]'. 

 The first of these ideas has led to no satisfactory solution of 

 the problem ; the second, however, reveals a constancy in the 

 chemical relations of the mineral which can scarcely be 

 regarded as due to accident. The relations in question are 

 shown by combining aluminium and iron with two hydroxyls 

 to form the groups [Al(OH) 2 ] and [Fe(OH) 2 ], respectively, and 

 copper with one hydroxyl to form the group [Cu(OH)], and 

 then finding the ratio between the phosphorus and [Al(OH) 2 ]' + 

 [Fe(OH) 9 ]' + [Cu(OH)]'H-Excess of hydrogen. The relations- 

 are shown by the ratios derived from the several analyses tabu- 

 lated on page 346, as follows : 





I. 





II. 





III. 



P 



•482 





•462 





•484 



Al(OH), 



•686^ 



•788^ 





•702 ^ 





Fe(OH)„ 

 Cu(OH)" 



■° 18 L 1-450 

 •108 f 145 ° 



•028 1 

 •066 f 



1-332 



•044 1 

 •096 f 



1-320 



H 



■638 J 



•450 J 





•478 J 





