The Extraction of Gold. 23 
The next question requiring attention was the best method 
of separating the sulphides from the waste tailings, and this 
has been found a difficult problem to solve. There is so 
little difference between the respective specific gravities of 
the quartz and iron pyrites, that the separation of one from 
the other in any known dressing machine, even with par- 
ticles of nearly the same size, would be imperfect. But this 
difficulty is vastly increased through the pyrites being more 
friable than the quartz, and therefore broken under the 
stamps into much smaller particles. ‘This difference in size 
counterbalances the difference in the specific gravities where 
water concentration only is used, thus nullifying the prin- 
ciple on which all the systems of ore dressing in general use 
are based. An attempt was made to classify the sand, but 
it was found that more than half the gold in the waste 
tailings was enclosed in particles of pyrites or sand in such 
a minute state of division that they could be passed through 
fine wire gauze having three thousand six hundred meshes 
to the square inch; and as it was evidently impracticable 
to pass one hundred tons of sand per day through sieves 
of this kind, the idea of direct classification was given up. 
A trial was made of the classifying boxes introduced by 
Mr. Ulrich, where the coarser sand and larger particles of 
pyrites pass out with the water flowing from a lower escape, 
and the lighter from an upper one. By this method the 
sand can be divided into several different qualities, but the 
classification is not according to size only, and is therefore 
imperfect. As mentioned before, the coarser particles of 
pyrites were retained on the blanket strakes, but the finer 
pieces floated away, and no dressing machine hitherto 
tried would retain more than a small proportion of these 
fine sulphides. The best result was obtained from the 
round concave buddle, with the improvements patented 
by Mr. Munday ; and this machine is now being worked 
to advantage at Clunes and other places, but it falls far 
short of the requirements of the case, and the endeavour 
to discover a better system has, in consequence, not been 
relaxed, 
After proving most of the known dressing machines, and 
many modifications of old plans, which it was hoped might 
overcome the difficulties in the way, without success, a trial 
was made of the percussion table, a dressing machine much 
used in Germany and South America. This is a table from 
ten to fourteen feet long and from four to six feet wide, slung 
