Easterfield and Aston. — The Chemistry of Bimu-resin. 483 



tion, and HON is evolved, which in its turn attacks the zinc 

 plates, or anodes, and combines therewith to produce addi- 

 tional double cyanide of zinc and potassium — ZnKoCN4. 



Thus, the solution during passage through the box is de- 

 prived of its copper, the place of the double cyanide of 

 copper and potassium being taken for an equivalent amount 

 of the double cyanide of zinc and potassium, from which latter 

 salt the cyanide may readily be obtained in the available form 

 of free potassium-cyanide by the method explained previously 

 in Case I. 



Should it be desired to ship the cyanogen product to 

 •market, it is shipped readily as the simple zinc-cyanide 

 ZnCy^, the precaution bemg taken to pack it, while damp, 

 in an-tight cases. When allowed to dry much of it is con- 

 verted to carbonate. To make the ZnCy^ available for gold- 

 extraction purposes it is, as previously explained, dissolved 

 in a caustic alkali, the excess of zmcate of soda or potash 

 being removed by addition of an alkaline sulphide. 



N.B. — It is advantageous, to promote perfect precipitation 

 •both in the precipitation of the cyanides with zmc salt and in 

 the precipitation of the zmc as ZnS, and in the electrical 

 precipitation of the copper and bullion, to cause active cir- 

 ■culation, which is best occasioned by the employment of 

 compressed au\ 



In the electrical precipitation-box the distance between 

 <jathode and anode should be ^ in. Beginning with a thick 

 plate of zinc and a very thin sheet of copper, you end with a 

 thin frayed sheet of zinc and a thick plate of copper con- 

 taining small amounts of bullion. 



Art. XLIII. — Studies on the Chemistry of the Netv Zealand 



Flora. 



By Thomas H. Easterpield, Professor of Chemistry in the 

 Victoria College, and B. C. Aston, Chemist to the Depart- 

 ment of Agriculture. 



{Read before the Wellington Philosophical Society, 2nd September, 



1903.] 



Part III. — Eimu-resin. 



The wide distribution of resinous substances in the vegetable 

 kingdom naturally raises three questions: (1.) What is the 

 function of resins in the plant-economy ? (2.) What is the 

 chemical origin of the resins? (3.) Are all the plant-resins 

 closely related from the chemical standpoint ? It is in the 

 hope of finding evidence which may help in arriving at an 



