324 NATURE'S TEACHINGS. 



wards, the powder was driven through the holes by the pressure 

 of the stone, and was afterwards separated into its various 

 degrees of fineness. 



I have only twice seen this process, and confess to have been 

 in a very nervous state on both occasions. The sieve is 

 whirled about with enormous velocity, and the pebble flies 

 round as if it were a thing alive. Let but a broken needle or a 

 fragment of stone get into the sieve, or even let the stone itself 

 break asunder, and there will be an instantaneous explosion, 

 which will hurl the house, the machinery, and the workmen 

 into unknown regions. 



Now, however, the mode of granulating powder is radically 

 altered. There is a series of double cylinders, such as shown in 

 the illustration, and each of them has the ridges cut into teeth 

 in regular order. Thus the first set of rollers or cylinders 

 merely bites the press-cake into convenient pieces, though 

 seldom of the same weight. 



The press-cake, thus bitten to pieces, is passed through a 

 series of cylindrical sieves, each graduated with the utmost 

 accuracy, and being turned by means of machinery. Being 

 set on a slope, the powder runs by its own weight down them, 

 and all those particles which cannot pass through the meshes 

 are poured out untouched at the lower end. 



The portions which are too large to pass the openings of the 

 first sieve are then handed onwards by means of a machine called 

 a " Jacob's Ladder," which consists of a series of little vessels or 

 buckets strung on a tape, and revolving over a couple of wheels. 

 The first set of buckets takes the coarsely bitten press-cake to 

 the second set of rollers, the teeth of which are comparatively 

 small. Thence it is passed over to a third set, and so forth, until 

 it is delivered in any quality of grain which may be required. 



The modern Mangle, again, affords a good example of this 

 principle. The old obtrusive, costly, and cumbrous Mangle, 

 which was nothing more than a heavy box of stones upon 

 rollers, has given place to the modern system of duplex action 

 in rollers, and one of the old Mangles is not easily to be seen, 

 unless it be worked as a curiosity. In fact, it is nearly as obso- 

 lete as the spinning-wheel, which yet may be seen in some of our 

 country villages, where scarcely one per cent, of the population 

 has ever been in a town, and many of them, the women espe- 



