Ford and Bradley — On Hydrozincite. 61 



Theory for 2ZnCO„.3Zn(OH) a . 



ZnO.. 74-14 



CO, 16-03 



HO -. 9-83 



100-00 



About thirty analyses of hydrozincite have been published 

 which have shown considerable variation, due largely doubtless 

 to the unsatisfactory character of the material examined. 

 Twenty-seven analyses were collected, more than half of which 

 are given in the fifth and sixth editions of Dana's System of 

 Mineralogy. These included the new analyses given below 

 together with all published analyses except such as showed 

 considerable amounts of unusual constituents. No other at- 

 tempt was made to consider them critically. The average of 

 these analyses is as follows : 



Average of 27 hydrozincite analyses. 



ZnO. 73-47 



C0 2 15-19 



HO . 11-24 



99-95 



This result does not agree very closely with our assumed 

 composition, but considering all facts is probably close enough 

 to lend support to that formula. In the great majority of 

 cases the material analyzed was amorphous in its structure. 

 Further, one of the constituents was unquestionably commonly 

 determined by the method of difference. It will be noted 

 that the average percentage of the most important and prob- 

 ably most accurately determined oxide, ZnO, is only about 070 

 per cent too low. 



It was felt that new analyses of the mineral, particularly 

 upon the crystallized material, would be of importance. Un- 

 fortunately the amount of material available was very limited, 

 which necessitated making the analyses on small amounts, 

 and the use of analytical methods which were not the most 

 desirable. Two different analyses were made on the mineral 

 from Good Springs, one on carefully selected material consist- 

 ing only of crystal fragments and the other on the crystalline 

 material that lay beneath the coating of crystals and which it 

 was felt might not be quite as pure. No evidence was found, 

 however, to show that there was any impurity present in the 

 latter material and as a larger amount of it was available for 

 analysis it is thought probable that its analysis is more nearly 

 correct than that of the crystals.. In order to experiment with 



