220 



easily applied ; its effect would be in relation to this sulphide, to decompose 

 it, and so expose the encrusted gold to the action of the mercury. 



Doubtless the great benefit which has often attended the use of this 

 amalgam has been principally due to the exercise of this kind of action.* 



Art. XXXVII. — On the Production of a Mono-hydrate of Chloride of Barium. 

 By W. Skey, Analyst to the Geological Survey of New Zealand ; with 

 Notes on its Crystallization, by E. H. Davis. 



(With Illustrations.) 



[Read he/ore the Wellington Philosophical Society, Sejyteviher 17, 1870.] 



In testing a mineral from the Thames gold-field containing baryta, I observed 

 that the chloride of this base deposited crystals from its hydrochloric acid 

 solution, differing considerably in shape from those described as belonging to 

 the common bi-hydrate ; they also difier in lustre, which inclined to pearly. 

 I therefore analyzed these crystals, and the results of this give the following 

 formula : Ba CI + HO. This is then a mono-hydi-ate of chloride of barium, 

 Avhich is the lowest hydrate yet obtained. 



Like the bi-hydrate, it effloresces in the air at common temperatures. 



The action of hydrochloric acid in determining the production of this 

 variety, is no doxibt referable to its affinity for water, this being superior to 

 that of the monohydrated salt. 



This salt has been microscopically examined by Mr. Davis, and the accom- 

 panying drawings of the crystals, and notes thereon, have been furnished by 

 him. 



On the Crystallization of Ba CI HO. 



The crystals are white and pearly, and effloresce rapidly ; they are 

 exceedingly small, requiring a high magnifying power to make them at all 

 distinct. The system is tetragonal, the same as the bi-hydrate of barium, 

 but, unlike that compound, all the ciystals are ditetragonal forms, or at least 

 have a combination of the ditetragonal and first kind of tetragonal, or of the 

 fii'st and second kinds. The relations of the parameters could not be deter- 

 mined for certain, for want of a proper instrument. 



PI. XX YI., fig. 1, is a ditetragonal pyramid, very perfect, having the 

 parameters as 1 : 1 : 2 as nearly as possible. 



Fig. 2, is a ditetragonal spheroid or ocalenohedron, its parameters are 

 nearly 1 : 1 : 2'5. 



* For further discussion of this subject, see N. Z. Geol. Sm-vey ReiJorts, 1870, p. 70. 



