558 Transactions. 



Fry, newly batched out. 

 „ second day, ventral aspect, yolk-sac uppermost. 

 „ third 

 „ fifth 



Plate LVI. 



Ammotretis rostratus, fry, eighth day after hatching 

 Blue-cod (Parapercis colias), egg ; x 20. 



,, larva just hatched out. 

 Pig-fish (Congiopodiis Icucopcecilus), just before hatching. 

 ,, larva, eighth day. 



Plate LVII. 

 Sketch-plan across Otago Harbour at Port Chalmers. 



Plate LVIII. 

 View of ponds, looking north-west to Port Chalmers. 



Pi ate LIX. 



Laboratory. 



Art. LXII. — On the Treatment of Partially Decomposed Pyritic 

 Tailings by the Cyanide Process. 



By H. Frank Shepherd. 



Communicated by Professor James Park. 

 [Bead before the Otago Institute, \Uh November, 1905.] 

 The first stage in the weathering of tailings or sands containing 

 sulphides of iron is the decomposition of the sulphides into 

 sulphates and free sulphuric acid. When clayey matter is pre- 

 sent in the sands sulphate of alumina is formed. The next 

 stage in the decomposition is the oxidation of the sulphates 

 into oxides. Consequently, when mineralised tailings have been 

 exposed to the weather for any length of time they will be found 

 to contain sulphates, oxides, and sulphides in various stages 

 of decomposition. 



Soluble sulphates and freshly formed oxides possess a much 

 more injurious effect on solutions of potassium-cyanide than 

 fresh, clean sulphides. Hence, in the treatment of piles of 

 mineralised tailings the first thing to be considered is the best 

 means of getting rid of the sulphates and oxides. 



The method of handling and successfully working old pyritic 

 tailings at our plant in Coromandel was as follows : With a 

 good jet of water the tailings were broken up and washed through 

 a ^ in. or fin. screen, then lifted with an ejector and run into 

 the tanks through a distributor. This broke up the material 

 and removed the sulphates, while most of the oxides, being 



