MICROSCOPICAL EXAMINATION OF FLOUR. 6 



PURPOSE OF INVESTIGATION. 



From the review of the literature, it is apparent that heretofore 

 the purpose of the microscopical examination of flour has usually- 

 been to determine the presence of adulterants, such as other flours, 

 or even starches, spores, etc. The paper in which Patterson indi- 

 cated the possibilities of an estimation of the offal content of a flour 

 microscopically (15) suggested the work here reported. 



MICROSCOPICAL METHOD. 



For convenience, the microscopical method employed in this inves- 

 tigation will he described under the following headings: (1) Appa- 

 ratus, (2) technique, and (3) counting bran particles and hairs. 



APPARATUS. 



1 . Microscopic slide with a ruled area about 22 millimeters square. 

 The lines, which it is convenient to have about £ millimeter apart, are 

 ruled across the short diameter of the slide. 



2. Cover glasses 22 millimeters square. 



3. Compound microscope, with compensating ocular 12 X and 16 

 mm. apochromatic objective. 



4. Scalpel, preparation needles, camel's-hair brush, spatula, alco- 

 hol lamp, mechanical stage. 



5. Assay balance. 



6. Chloral hydrate solution about 1:1; preferably not any more 

 concentrated. 



TECHNIQUE. 



Before undertaking the examination of a flour microscopically, the 

 sample should be thoroughly mixed, and a composite sample with- 

 drawn from various parts of the material. A 5-milligram portion of 

 flour is carefully weighed out upon accurate balances, and the weighed 

 portion transferred to the center of the ruled area on the microscopic 

 slide. The scalpel is employed in removing flour from the weigh- 

 ing pan to the slide, the small amount which can not be thus re- 

 moved being easily brushed onto the slide with the camel's-hair brush. 

 The flour being transferred to the slide, about 3 or 4 drops of chloral 

 hydrate solution are mixed with the flour by means of the preparation 

 needle. Add only enough chloral hydrate solution to fill the space be- 

 neath the cover glass. The proper amount is usually about 4 drops 

 when a pipette with a 1 -millimeter bore is employed. A pipette of 

 larger bore releases too much solution at a time and is less convenient 

 to control. It is important that the material be evenly distributed in 

 the solution; otherwise flocculation of the flour will occur, rendering 

 counting more difficult and less accurate. The square cover glass is 

 next applied, and the slide heated over the alcohol flame until the 



