Penfield — Chemical Composition of Turquois. 349 



VII. 

 •404 



•742] 



' 05 ° I 1-262 

 •083 I i ZbZ 



•387 J 



Considering [Al(OH 2 ]' + [Fe(OH) s ]' + [Cn(OH)]' + H' as play- 

 ing the role of a univalent radical R', the ratios of P : R in the 

 several analyses are as follows: 





IV. 



V. 



71. 



p 



•468 



•450 



•464 



Al(OH), 



•706] 



•774] 



•722] 



Fe(OH) 

 Cu(OH) 



•098 f l 478 



•080 \ 1>426 



•572 J 



•030 1 



•094 f * 428 



H 



•638J 



•582 J 



I, 



P : 



R = 



•482 



; 1-450 = 1 



3-01 





II, 



(C 



» 



•462 



1-332 = 1 



2-88 





III, 



tc 



a 



•484 



1-320 = 1 



2-73 





IV, 



« 



a 



•468 



1-478 = 1 



3-16 





v, 



cc 



a 



•450 



1-426 = 1 : 



3-17 





VI, 



a 



tc 



•464 



; 1-428 = 1 



: 3-08 





VII, 



a 



a 



•404 



1-262 = 1 ; 



3-12 



Average = 



1 : 3-02 



The author can vouch for the purity of the material analyzed 

 by him, as far as it is possible to do so in the case of a crypto- 

 crystalline mineral, and can also testify as to the accuracy of 

 the analysis, and the very close approximation to the exact 

 ratio 1 : 3, between the phosphorus and the sum of the univa- 

 lent radicals plus the hydrogen, is very suggestive. The ratios 

 in the other analyses approximate as closely to 1 : 3 as might 

 be expected when the character of the material is taken into 

 consideration, and the average of all the ratios is almost exactly 

 1 : 3. The ratio 1 : 3 is that of phosphorus to hydrogen in 

 ortho-phosphoric acid, H 3 P0 4 . Turquois may therefore be 

 regarded as a derivative of ortho-phosphoric acid in which the 

 hydrogen atoms are to a large extent replaced by the univalent 

 radical [Al(OH)J, [Fe(OH) 2 ] and [Cu(OH)]. There seems to 

 be no fixed ratio between the radicals [Al(OH) 2 ], [Fe(OH)J 

 and [Cu(OH)], nor between the sum of the hydroxyl radicals 

 and the hydrogen. In some cases, however, there is an 

 approximation to the ratio 2 : 1 between the sum of the 

 hydroxyl radicals and the hydrogen, as follows : 



[Al(OH),] + [Fe(OH),] + [Ca(OH)] : H 



II, -882 : -450 = 2 



III, -844 ; -478 = 2 

 VII, -875 I -387 = 2 



In cases like the foregoing, the composition of turquois 

 might be considered as a mixture of an aluminium salt, 

 H[A1(0H) 2 ] 2 P0 4 , with the isomorphous molecules HfFe^EL),], 

 P0 4 and H[0u(OH)] 2 PO 4 . The molecule H[A1(0H) 2 ] 2 P0 4 is 

 equivalent to Clarke's formula for "normal turquois," 2A1 2 S . 

 P 2 6 . 5H 2 0, which he also writes A1 2 HP0 4 (0H) 4 . Adopting 



1-02 

 1-13 

 0'89 



