736 SUMMARY OF CURRENT RESEARCHES RELATING TO 



gold in iron pyrites, which we now know to exist in a metallic state, 

 being therefore only mechanically mixed with the iron pyrites, so that 

 the amalgamation of the gold in the raw ore can be easily effected, 

 and with little loss, if ordinary precautions are taken to have the ore 

 reduced fine enough to liberate the gold enclosed in the finer particles 

 of pyrites. Mr. Atwood procured samples of pyrites from most of the 

 mining counties of this State, and made a careful microscopical 

 examination of them, the result confirming in every respect the 

 conclusions of Daintree and Latta published in Australia in 1874. 



The paper was illustrated with several mounted specimens. One 

 slide showed the gold on a crystal of pyrites, which, with the aid of an 

 inch objective, was seen as a beautiful gilding on some of the planes 

 of cleavage. Another slide showed the gold in little drops, also filling 

 some of the small cavities. Still another showed the gold in little 

 specks, imbedded in the pyrites. Another specimen disclosed the gold 

 in fine specks or scales mixed with the sesquioxide of iron. Mr. 

 Atwood has found that in the examination of all metals good bright 

 daylight should, if possible, be used. The specimens, as seen by 

 lamplight, did not exhibit the gilding as well as it was seen in the 

 daytime. 



Micro-Chemical Methods for Mineral Analysis.* — T. H. Behrens 

 publishes a very full paper on this subject, commencing with an 

 historical account of the origin and progress of micro-mineralogical 

 methods, and with a detailed description of his " new micro-chemical 

 method," 



If, he says, the number of micro-chemical reactions which are at 

 the disposal of the microscopist in the subject of petrography is 

 much smaller, and their application is much more limited than in 

 the microscopical anatomy of plant and animal tissues, the reason is 

 certainly not that less advantage may be expected from the examina- 

 tion of the rocks by such methods. If in felspar the potassium and 

 calcium could be detected with the same ease and certainty and their 

 quantity appropriately ascertained, as is done in the case of starch by 

 means of iodine, and of cellulose by means of iodine and sulphuric 

 acid, how much petrography would be advanced by such a method of 

 examination will be evident to most microscopists. 



Endeavours were early made to extend the means of determining 

 the constituents of rocks. Zirkel first examined his rock sections in 

 ordinary light, then in polarized light, and in 1868-70 he introduced 

 hydrochloric acid as a reagent to distinguish between decomposable 

 and undecomposable minerals in basalt, viz. labrador from oligoclase 

 and magnetite from titanic iron. Since then this acid has had its 

 use extended, but only in a few cases were the products of the reaction 

 subjected to examination, thus the formation of carbonic acid, of 

 sodium chloride and of gelatinous silica, capable of taking up colour- 

 ing matters, were used to demonstrate the presence of calcite, nepheline 

 and decomposable silicates as olivine, chlorite, &c, respectively. Other 

 micro-chemical reactions are the detection of apatite by a nitric acid 



* Versl. en Mededeel. K, Akad. Weteusch, xvii. (1881) pp. 27-73 (1 pi.). 



