Modem Improvements in Corn-Milling Machinerij. 103 
of air exactly proportioned to tlie specific gravity of the semo- 
lina or middlings to be treated. Tlie separation into sizes is 
accoraplislied by sizing reels or sieves. And that there may be 
no waste, by reason of flour-dust being carried off by the air 
currents, it is of the greatest moment that all the semolinas and 
middlings should be perfectly freed from all floury particles 
before they enter the purifiers. 
The importance of the purifying operations in " gradual 
reduction " cannot be exaggerated. It is the foundation of the 
success of the whole process. By purification a certain portion 
of the flour-bearing cells of the wheat-corn can be completely 
freed from the contamination of bran, and other portions can in 
various degrees be made more or less free. From these pure 
middlings the highest quality flours are produced, and the aim 
and object of the miller is, by skilful manipulation of his machi- 
nery, to obtain from wheat the greatest possible percentage of 
pure flour, to be sold either as fine flour (and called, after an 
American fashion, " Patent'"), or to be mixed with the various 
lower qualities, which the mill must produce from the less pure 
middlings and in the breaking process, and form what is called 
" straight grade " or " straight run." While the '■ purifier " by 
enabling the miller to get rid of the admixture of bran specks 
from the middlings laid the foundation of the process, the use 
of the smooth roller-mill has been of immense advantage in the 
same direction by its operation in breaking down or reducing 
middlings containing bran specks to flour without cutting up 
the branny particles to the same extent as millstones. 
The stage has now been reached in our account of the 
process when the semolinas and middlings obtained in the 
"breaks" may be supposed to have been purified and to be 
ready for reduction to flour. The reduction of these is accom- 
plished in much the same manner as the " breaking " of the 
wheats. Each size of purified semolina or middlings should be 
cracked down on separate roller-mills ; the flour produced in the 
passage between the rollers is to be sifted or dressed out. If the 
particles remaining be still of sufficiently large size, they should 
be re-purified, and passed on to other rollers, and then the 
produce of those rollers is re-dressed, flour removed, and the 
" gradual reduction " is repeated until no flour of value above 
the worth of ofl"al can be obtained. But throughout this mid- 
dlings reduction, there is a possibility of separating and remov- 
ing branny matter at each purifying and at each grinding 
operation, and the most is made of these opportunities. Each 
different quality of middlings and each grinding yields a flour 
of different quality, and these flours can be kept separate for sale, 
or combined in any proportions that may suit the trade or 
