221 



Fig. 3, is a ditetragonal prism, broken at one end, and terminated at tlie 

 other by an obtuse pyramid. 



Fig. 4, is similar to Fig. 3. 



Fig. 5, is a combination of a primary prism with a prism of the second 

 kind, apex being the pyramid of the first kind. 



Fig. 6, is interesting, as it presents the curious marking hitherto (I believe) 

 peculiar to chiastolite, which is a rhombic crystal. 



Fig. 7, is a normal prism terminated by a pyramid, having its angles 

 replaced by a more acute jjyramid of the second kind. 



Fig. 8, is a combination of a primary prism having an acute pyramid 

 capped by one more obtuse, which is again terminated by a pinacoid ; this 

 crystal is either one which has lost its water of crystallization, or, what is more 

 probable, it has absorbed one equivalent from its neighbour, which was quite 

 opaque to polarized light. 



Fig. 9, represents two crystals, both perfect, consisting of combinations of 

 primary and secondary prisms and pyi'amids. 



All these were carefully examined and drawn while under the microscope ; 

 they present no features by which they could be certainly recognized from 

 some other salts, but as a new compound, it is interesting to observe the com- 

 plete change in the style of the crystallization which one eqixivalent of water 

 can cause. 



Art. XXXVIII. — Researches on the Absorptive Properties of Platinum. 

 By W. Skey, Analyst to the Geological Survey of !N"ew Zealand. 



[Bead before the Wellington Philosophical Society, October 22, 1870.] 



The researches embodied in this paper were collateral with those given in 

 Art. XXXYII. in point of time, and of a kindred nature, but I preferred to 

 state the results of them separately, as the subject itself is foreign to gold 

 mining interests, to which the other appears intimately connected. 



Shortly stated, these results are as follows : — 



When a piece of freshly-cleaned platinum is placed in the vapour of 

 sulphuretted hydrogen, or in solution of sulphide of ammonium, at common 

 temperature for a few minutes, then well washed in distilled water, it will be 

 found to have acquired such a condition upon its surfaces that metallic contact 

 cannot be established between it and mercury ; whereas, before treatment with 

 these sulphur compounds, amalgamation rapidly proceeded over the whole 

 surface of such piece on the application of mercury. 



When the sulphixretted hydrogen was thoroughly dessicated, before 

 administration to the platinum, amalgamation was neither prevented nor 

 retarded ; at least, I could not observe any such effect. 



