174 



Art. XLII. — On Improvements in the Processes for Extracting and Saving 

 Gold. By T. Heale, C.E. 



[Read before the Auckland Institute, November 15, 1869.] 



The quartz crushing machinery at the Thames is very excellent, and the 

 appliances used for saving the gold ore are, I have no doubt, on the whole, as 

 effective as is possible, consistently with the rapidity and economy required. 



Nevertheless one occasionally hears instances of exceedingly conflicting 

 and unexpected results — thus I find in a paper published a few days ago : 



" Clarkson's machine. — One parcel of calcined stuff from the 'John 

 O'G-roat,' weighing only 11 tons, yielded lloz. 4 dwt. retorted gold. Another 

 parcel of 11 tons uncalcined yielded 22 oz. 14 dwt., and 2 tons uncalcined stuff, 

 crushed in the single stamper, yielded 8 oz. of gold. The battery is now 

 crushing a 30 ton lot for the ' Pukehinau.'" 



I am informed that care was taken that these several parcels should, as 

 far as possible, be of uniform quality. And, in this Institution, on the 5th 

 October, last year, a discussion arose in which it was stated that the use of 

 the water from one source, as compared with another not apparently purer, 

 caused a difference of one-third in the quantity of gold obtained.* Nor is it at 

 all wonderful that occasional failures to save the gold by amalgamation should 

 take place, when it is considered that for the amalgamation to be complete, 

 every particle of gold must be brought into actual contact with mercuiy, the 

 minutest tilm on the surface of either metal being sufficient to prevent their 

 union j a circumstance ■which may arise either from the sickening of the 

 mercury, as it is called, or from the gold having become coated with some 

 repelling film derived from the liquids— as in the case named by Mr. Whitaker 

 — or from the gases evolved in calcination, as in the case referred to from the 

 "John o' Groat." 



What then, in my opinion, is wanting is, not any improvement in the 

 machinery and appliances now in use, so much as a ready and certain means of 

 ascertaining by assay — which shall be trustworthy and at the same time not too 

 expensive — whether or not the process is going on rightly, and all, or the great 

 majority, of the gold present in the material is being saved ; since if it should 

 be found that appreciable portions of the gold are passing away with the 

 tailings, it will generally not be difficult to ascertain the cause of the evil, and 

 to apply an appropriate remedy, such as cyanide of potassium, or Mr. Crook's 

 sodium amalgam, if the failure appeared to arise from the sickening of the 

 mercury ; or to a different treatment of the quartz, or the use of other waters, 

 if the fault appeared to lie in their conditions. 



The subject to which I wish to draw attention, and on which T would 

 invite discussion, is the practical methods of assaying quartzoze and earthy 

 matters supposed to contain small portions of gold. Now since the commonest 

 observation shows that gold is never equally distributed through the mass, and 

 since it is probable that after every care in pulverization the gold may still 

 remain in particles of appreciable size, it follows that a very small sample can 

 never be depended upon as representing the mass, and therefore that the 

 delicate"~analytical processes of the chemist, which can only be used on very 

 small quantities, are not adapted to the practical uses of the gold-miner. Now 

 1 oz. of gold to the ton is equivalent to 1 part in 32,666, or 1 grain in 4|lbs. 

 avoirdupois, therefore it is convenient to take this quantity, or an aliquot part 

 of it, for the assay, and in practice I think one-fourth of it, or l^lb. will be 

 found the smallest from which satisfactory results may be obtained, since in 

 that quantity one-eightieth of a grain of gold will represent 1 dwt. to the 

 ton. 



* See "Trans. New Zealand Institute," Vol. i., p. 72. 



