122 



Journal of Applied Microscopy. 



never been repaired, and while not so 

 fresh looking' as when new, they are still 

 quite presentable in appeai'ance. During 

 this time, the toys have undergone very- 

 hard usage. Strong acids, as sulphuric, 

 nitric and hydrochloric, intense stains 

 like carbol-fuchsin and haematoxylin, 

 concentrated potash solution, alcohol 

 from lamps, as well as various other 

 corrosive and staining reagents, have all 

 been spilled upon the tops, often in large 

 quantities, and but very little damage 

 has resulted. Oftentimes the reagent 

 has left no trace whatever. Then, too, 

 heavy microscopes, dissecting pans, and 

 trays have been moved roughly about, 

 leaving few if any marks. Besides being 

 easily cleaned from stains, fragments of 

 tissue, and so forth, the black surface 

 makes an excellent background, against 

 which light-colored objects, as small 

 alcoholic specimens for dissection, 

 stand out distinctly. There is, further- 

 more, no reflection to interfere with 

 careful illumination of objects under 

 the microscope. For general purposes, 

 where many kinds of work must be done 

 on the same tables, as is the case in all 

 the smaller institutions, it is thought 

 that the best satisfaction will be given 

 by tables prepared as described above. 

 The treatment is cheap, durable, and 

 serves a number of purposes. 



Charles Wright Dodge. 

 University of Rochester, 



pearance of the maize srarch grains 

 somewhat more definite. If 20 cc. of this 

 liquid be used for one gram of the 

 sample, a mixture will be obtained hav- 

 ing about the proper dilution for the 

 ready counting of the grains under the 

 microscope. The eyepiec"e of the mi- 

 croscope used was provided with a mi- 

 crometer ruled in squares one mm. on a 

 side. There were twenty-five of these 

 squares in the central part of the field. In 

 the case of each preparation the grains 

 were counted within the limits of these 

 twenty-five squares, and the slide was 

 moved so as to bring the next adjoining 

 area of the same size in the position oc- 

 cupied by the grains just counted. This 

 was repeated until five fields had been 

 counted. The average ratios for each of 

 the six known mixtures and for the 

 three unknown mixtures were as follows: 



A Note on the Quantitative Deter- 

 mination of the Adulteration of 

 Wheat Flour with Maize Pro- 

 ducts. 



It is the purpose of this note to report 

 the results of experiments made to de- 

 termine the degree of accuracy which 

 can readily be obtained in the deter- 

 mination of the percentage of adultera- 

 tion of wheat fiours with maize starch 

 or maize flour. For this purpose six 

 mixtures of high-grade maize starch 

 with wheat flour were prepared, con- 

 taining five, ten, twenty, thirty, forty 

 and fifty per cent, of maize starch re- 

 spectively. Three more mixtures were 

 prepared from the same materials, in 

 proportions unknown to the operator. 



One gram of each mixture was care- 

 fully mixed in a small beaker with 20cc. 

 of the following mounting medium: 



Glycerin, 2 volumes. 



Glacial acetic acid, 1 volume. 



Distilled water, 1 volume. 



The glycerin prevents the rapid evap- 

 oration of the mounting fiuid, while the 

 acetic acid renders the characteristic ap- 



The percentage of corn starch in each 

 unknown mixture was calculated on the 

 basis of the ratios obtained for each 

 of the known mixtures, except that in 

 the cases of mixtures A and C the ratio 

 for the known mixture containing five 

 per cent, of corn flour was omitted. 



Mixture A. — Ratio of number of maize 

 starch grains to number of wheat starch 

 grains was found to be 1:20.6. The ratio 

 obtained for the 10% mixture indicates 

 that this sample contains 28.8% of maize 

 starch; the ratio for the 20% mixture in- 

 dicates 29.7%; the ratio for the 30% mix- 

 ture indicates 27.8%; the ratio for the 

 40% mixture indicates 26.4%; and the 

 ratio for the 50% mixture indicates 

 34.0%. The average of these is 29.3%. 

 The theoretical percentage of maize 

 starch in mixture A was 32.5%. 



Mixture B. — Mixture B gave the aver- 

 age ratio of 1:195.7. The ratio obtained 

 for the 5% mixture indicates that mixture 

 B contains 7.05% of maize starch; the 

 ratio for the 10% mixture indicates 

 3.03%; for the 20% mixture, 3.64%; for the 

 30% mixture, 2.93%; for the 40% 

 mixture, 2.77%; and for the 50% mixture, 

 3.57%. The average of all of these is 

 3.83%. The theoretical percentage of 

 corn starch in mixture B was 7.75%. 



