104 DRESSING OF ORES 



In addition, Mr. Smyth gives the following particulars of cost of crushing quartz and 

 extracting the gold : 



Dallarat Clunc* Sandhurst Maryborough Ca.tlomsino Maldon 

 Average cost of raising and delivering 



one ton of quartz at the mill . 5/10* 12/10 to 27/1 8/10J 21/8 7/8J 27/4 



Stamping quartz and extracting gold 2/10 7/5 2/9fc 8/ 3/9 14/4J 



The following are among some of the advantages afforded by the stamping mill : 

 (1.) It gives a direct dead blow, highly effective in reducing semi-elastic minerals; 

 (2.) The force of the blow can be readily modified by shifting the position of the tap- 

 pet ; (3.) The free fall of the head is entirely exerted on the stuff, and its effect is in 

 no way transferred to the framework or other parts of the apparatus ; (4.) The repairs 

 required are few and simple, such as an ordinary mine smith and carpenter can execute ; 

 (5.) A battery of heads may be stopped and repaired while the others are running; 

 (6.) Single heads may be thrown out of use without affecting the working conditions 

 of the mill; (7.) The mineral under treatment receives the least possible handling, 

 and can be flumed at once either to dressing or amalgamating apparatus ; (8.) Minerals 

 can be readily reduced to a condition of fine sand, provided the faces of the heads 

 are good ; (9.) Speed, lift, the weight, size, form of head, position of discharge, and 

 extent of grate way, admit of numerous variations to suit the condition of different 

 minerals, and afford a wide field for the exercise of intelligence, judgment, and practical 

 skill. 



Pneumatic Stamps. The ordinary form of stamps, as used in the county of Cornwall, 

 is a simple and very old type machine. 



It consists of heavy cast-iron heads, about 6 cwts. each, fixed on wrought-iron 

 square shanks, a projecting tappet attached to the upper part of the lifter, against 

 which the revolving cams come into contact, raising the lifter and liberating it at 

 the height of 10 inches; the heavy head then falls by its own gravity, and im- 

 pinges with considerable force the crushing blow on the ore beneath it in the 

 coffer. 



The greatest speed to which these stamps can be driven is about 60 blows per 

 minute; and consequently in tin stamping, the heavy particles of tin ore, although 

 reduced to sufficient size to pass through the grate holes, by not being kept sufficiently 

 agitated, settle to the bottom of the coffer, and there get further pulverised, thus 

 causing the formation of a considerable quantity of slime, which is far from desirable, 

 and entails considerable loss in the process of dressing. 



This ancient form of stamps is a rude primitive machine, and something more 

 effective should be looked for in these days of mechanical refinement. 



If a man were to set about pulverising a stone, it is evident that he would not 

 take a large heavy hammer, of say 25 Ibs. employ all his strength in raising the 

 hammer a few inches, and allow it to fall of its own weight ; but with a much 

 lighter hammer, with quicker blows, and using his muscular strength on the downward 

 blow, he would get far better duty with the same expenditure of power. And so with 

 the machine for obtaining the same end, a lighter head should be used and force em- 

 ployed in the downward blow. 



To meet these discrepancies, evident and important as they are, the pneumatic 

 stamps has been devised. 



As early as 1856 the idea was conceived of employing an air-sponge or cushion in 

 the working of steam-hammers, by Mr. Carr, an Englishman ; since then, many 

 patents have been taken out for various plans of employing springs, and air-cushions 

 for hammers. 



The same principle applied for stamping purposes is employed in the pneumatic 

 stamps patented by Mr. W. Husband of Hayle, Cornwall. 



These stamps, generally two heads to the coffer, consjst essentially of a cast-iron 

 crank, to which is attached by means of a forked connecting-rod, a pneumatic cylinder ; 

 the stamps' lifter is a hollow turned wrought-iron shank, fixed to head, with a metallic 

 piston attached ; the piston works in the air cylinder, with the lifter projecting through 

 either end, and the head operating in a closed cast-iron coffer. 



A rotatory motion being given to the crank, the cylinder is raised, the air it contains 

 becomes compressed beneath the piston and the lifter with head attached, about 

 310 Ibs. raised to the height of about 16 inches ; as soon as the crank turns the centre, 

 the compressed air yields back the force employed in its compression, and consequently 

 a violent blow is given on the coffer. 



A stream of water flows through the hollow lifter, discharging above the head into 

 the coffer : this serves the double purpose of removing the heat generated through 

 the compression of the air, and for providing the necessary water for stamping 

 purposes. 



Another object in making the lifter hollow, is to prevent crystallisation of the iron, 



