GRINDING AND CRUSHING MACHINERY. Most of the improvements in grinding and crushing machines have been made within the last 30 years, particularly as relates to crushing and breaking. Until the development of the gold fields of Cali fornia subsequent to the year 1849, in which was the commencement of the great migra tion thither, the breaking of stones and ore was performed usually by hand, with a sledge, in connection with blasting. The first machine on the Pacific coast consisted of immense weights, raised by cams to a height of 4 or 5 ft., and let fall upon the rock. A machine leaving a weight of one ton had a capacity of breaking one ton of quartz rock an hour. There was no mortar or trough. but the rock was placed on the face of an anvil, around which there was a grating through which fell all the pieces broken sufficiently fine. Coarser pieces could be replaced upon the anvil. A machine more easily worked, and very effective, was invented by Mr. Eli Whitney Blake, of New Hayan. Conn. A very heavy, stationary, vertical plate forms one side of a wedge shaped hopper, which is at the same time the crushing chamber. The other side of the hopper is formed by a movable jaw which turns upon a pivot at the upper end, the lower end coming as near the stationary piece as the required size of the fragments. This jaw is moved backwards and forwards through the space of about one quarter of an inch, by means of a toggle joint Wilk:111S moved by a wheel. A rubber spring aids in draw ing the jaws apart suddenly, thus facilitating the descent of the rocks in the wedge shaped hopper. The product of crushed matter varies with the different sizes from 3 to 7 cubic yards per hour, the horse-power varying from 4 to 12. Hall's breaker is a modification of Blake's, the movable jaw consisting of two pieces which play alternately. For further notice of rock-crushing machinery-, see METALLURGY, and for sugar-cane crushing-machines, see SUGAR. In the article MILL there is a description of grind
stones and machinery for making flour. There are various other forms of mills for other purposes, such as the crushing of seeds and bark, and grinding of paints. Very power ful mills are required in the preparation of vulcanized India-rubber (caoutchouc). The crude India-rubber, after being boiled and softened in a steam vat, is passed between two fluted rollers of very great strength, by which it is ground to a sort of paste. A kind of mill used for crushing seeds, grinding chocolate, mixing mortar, etc., consists of two vertical wheels turning independently upon the ends of an axle, which also turns upon a vertical pivot midway between the two wheels. A circular bed or vat, having a rim of greater or less height, receives the article to be ground, over which the wheels or rollers are made to revolve. One of the most ingenious, simple, and effective mills in use was the invention of Mr. James Bogardus, of New York city. Two wheels, having on their faces concentric grooves, have different axes of revolution, being eccentric, a name given to the mill. The wheels are placed horizontally, and the lower one is turned by a shaft at the rate of from 600 to 800 revolutions per minute. The upper wheel also takes on a motion from the impulse of material brought against it, but being eccentric, the material is brought diagonally against the edges of the groove, making the grinding very effective and preventing clogging. Over 200 barrels of sugar have been ground per hour in a 16-in. mill. It will grind 5 tons of oil-cake, half a ton of bark, two tons of white lead in oil, four tons of iron-ore, and two tons of any ores per hour. It is very strong and not easily disordered.