436 



SCIENTIFIC NEWS. 



[May II, 1888. 



meal from which the bran has been sifted while the 

 poUard remains. Besides the above-stated constituents 

 of pollard it contains a small quantity of ccrealine, which, 

 according to some good authorities, acts like the diastase 

 of the saliva in converting starch into sugar. If this be 

 correct, it not only adds to the nutritive value of the 

 bread by its own direct contribution of nutritive material, 

 but it also renders the other portion more nutritious by 

 assisting its digestion. Such bread as I propose is of 

 excellent flavour, but of rather dark colour. 



THE STURTEVANT CRUSHING AND 

 GRINDING MILL. 



'T'HE Sturtevant mill is an American invention used 

 for crushing and grinding ores, cements, phos- 

 phates, emery, and such like hard substances. For work 

 of this kind there are usually two operations ; first, the 

 crushing, then the grinding, and generally this is 



to grind against each other. The speed varies from 900 

 to 1,800 revolutions a minute, according to the size of 

 the machine, and at this high speed the grinding 

 force is very considerable, and showers of sparks 

 can be seen inside the mill. The rapidity with which 

 the work is done can be best imagined when we say 

 that we have seen, at the works of the Lawes Chemical 

 Manure Company, at Barking, a mill twenty inches in 

 diameter, crush and grind large pieces of phosphate rock 

 from South Carolina, at the rate of about fifteen tons an 

 hour — about 25 per cent, leaving the mill as fine powder, 

 the remainder being coarse powder, mixed with pieces 

 not larger than peas. Judging by the freedom of 

 the shafts when running, the horizontal thrust on the 

 cups appears to be slight, and a remarkable feature is 

 that a very short time after the mill has been started a 

 hard deposit of ground material is formed on the inside 

 of the cups, and assumes a conical shape as shown at 

 ZZ in Fig. 3. This deposit adheres tenaciously to the 

 cups, and is so hard that it can only be removed with 



Fig. 3. — Sectional View of Interior of Mill. 



done in separate machines. In the Sturtevant mill the 

 crushing and grinding are effected simultaneously in one 

 machine of small dimensions and of very simple con- 

 struction, and the speed with which it does its work, 

 with very little wear and tear, is certainly remarkable. 



Fig. I represents the mill in operation, the material to 

 be ground being fed into the open hopper at the top of 

 the casing A, and passing out when ground through the 

 bin D. The driving pullies are on separate shafts, and 

 on the end of each shaft is a hollow cup B, the edge of 

 which just enters the side opening in the casing A. Fig. 

 2 represents the cups drawn back from the casing, and 

 shows a circular grating or screen C inside the latter. 

 Fig. 3 is a sectional view of the two cups, and of the 

 interior of the mill when charged with material to be 

 ground. 



We are informed that with the smaller sizes of mills 

 the two cups are sometimes driven in the same direction, 

 and sometimes in opposite directions ; but in the large 

 sizes it is usual to drive them in the same direction 

 and at the same speed. As the material passes through 

 the mill it is crushed and pulverised, not by grinding 

 against the surfaces of the machine, but by the 

 force with which the pieces of rock, etc., are made 



difficulty, and it protects the iron most effectively; in fact, 

 the edges of the cups, and to a less extent the screen C, 

 are the only parts of the inside of the mill which are 

 liable to wear. The cups are made of chilled cast-iron, 

 and when the edges are worn the shafts are moved a 

 little nearer to the casing, the bearings of each shaft being 

 fixed to a moveable base for this purpose. 



In connection with the mill there is a rotary fan which 

 causes a strong current of air to be drawn downwards 

 through the mill, and in this way it is kept 

 cool, while at the same time all escape of dust 

 is prevented. During the working of the 20-inch 

 mill above referred to, although the interior was full of 

 sparks caused by the violent contact of the pieces of rock, 

 the casing A was cool, and the ground material which 

 fell from the bin was only slightly warm. 



The makers have a theory that each of the rotating 

 cups sets up a centrifugal force, which hurls its contents 

 against those of the opposing cup. Seeing, however, 

 that the capacity of each cup is small, especially when 

 the deposit Z has been formed — and that between the 

 cups there is the mill itself, which is charged with 

 material, as shown in Fig. 3 — there is little probabiUty 

 that the pieces can be thrown about in the manner sug- 



