568 MINING INDFSTEY. 



tables without satisfactory treatment, would be certainly collected for a subse- 

 quent and more effective process. 



Further, by providing proper means of concentration which should save 

 all, or nearly all, the valuable portion of the crushed product, the capacity or 

 duty of the stamps could be greatly increased, and the expense, per ton, be 

 thus considerably diminished. It has been pointed out that the speed of the 

 stamps is very low, some making only 15 drops per minute, and the average, 

 in the district, probably not exceeding 28 drops per minute. With this speed 

 the amount crushed is, on the average, less than one ton, per stamp, per day, 

 and probably less than one-half the average quantity crushed, per stamp, in 

 any other extensive mining region in the country, where a similar method of 

 wet-crushing is employed. It is obvious that, if the quantity of rock crushed, 

 in a given time could be doubled without much increasing the cost of labor, 

 fuel, or other materials, the expense, per ton, would be very largely reduced. 

 It is urged by many that the necessity for slow crushing is due to the peculiar 

 condition of the gold, which, it is said, requires a long time for amalgamation 

 in the battery. However this may be — and some experience already noted 

 on page 555 makes it doubtful — it is still probable that the increased per- 

 centage of gold saved by protracted crushing is a comparatively insignificant 

 proportion of the whole amount obtained, and might be more economically 

 saved by appliances provided outside the battery. In this particular, im- 

 proved methods of concentration would to be useful. 



Some experiments were made last summer, at the Black Hawk mill, with 

 the view of adopting improved concentrating machinery. A Rittinger per- 

 cussion table was constructed and set up outside the building, and a lot of 

 tailings were treated upon it. The table was not advantageously placed, nor 

 established under so favorable conditions as would be provided for permanent 

 use, but the results obtained, with the experimental lots that were worked 

 were very satisfactory, and it was then decided to build a sufficient number 

 and place them in the mill in front of the batteries and short amalgamating 

 tables, so that the crushed ore, after having yielded what it might to the 

 quicksilver, could pass at once on to the tables and there be concentrated. 

 The writer has been unable to learn under what conditions these tables were 

 set up, or with what degree of success they have been operated; but the very 



