MICROSCOPICAL STUDIES ON TOMATO PRODUCTS. ae 
METHOD FOR MICROANALYSIS OF TOMATO PRODUCTS. 
Since the publication of Bureau of Chemistry Circular 68 no state- 
ment of the microscopical method used by the department has 
been issued. The bureau has received repeated requests for a 
restatement of the method, including more definite details of 
manipulation than were given in the circular. In 1915, after the 
method incorporating the most important of these details had been 
rewritten, the Association of Official Agricultural Chemists adopted 
it as a tentative method and published it November, 1916, in the 
Journal of the Association of Official Agricultural Chemists. At the 
meeting of the same association in November, 1916, a few minor 
changes were authorized. As it is uncertain when the association 
will publish the method in its amended form, permission has been 
eranted by the chairman of the Board of Editors of the Association 
of Official Agricultural Chemists to incorporate it here. 
491 APPARATUS. 
(a) Compound microscope-—Equipped with apochromatic objectives and compen- 
sating oculars, giving magnifications of approximately 90, 180, and 500 diameters. 
These magnifications can be obtained by the use of 16 and 8 mm Zeiss apochromatic 
objectives with X6 and X18 Zeiss compensating oculars, or their equivalents, such as 
the Spencer 16 and 8 mm apochromatic objectives with Spencer X10 and X20 com- 
pensating oculars, the drawtube of the microscope being adjusted as directed below. 
(6) Thoma-Zeiss blood counting cell.” 
(c) Howard mold counting cetl.—Constructed like a blood-counting cell but with 
the inner disk (which need not be ruled) about 19 mm in diameter.? 
501 MOLDS (TENTATIVE). 
Clean the special Howard cell so that Newton's rings are produced between the 
slide and the cover glass. Remove the cover and place, by means of a knife blade or 
scalpel, a small drop of the sample upon the central disk; spread the drop evenly over 
the disk and cover with the cover glass so as to give an even spread to the material. 
It is of the utmost importance that the drop be mixed thoroughly and spread evenly; 
otherwise the insoluble matter and consequently the molds are most abundant at the 
center of the drop. Squeezing out of the more liquid portions around the margin 
must be avoided. In a satisfactory mount Newton’s rings should be apparent when 
finally mounted and none of the liquid should be drawn across the moat and under 
the cover glass. 
Place the slide under the microscope and examine with a magnificaticn cf about 
90 diameters and with such adjustment that each field of view represents approxi- 
mately 1.5 sq. mm of area on the mount.? This area is of vital importance and may 
be obtained by adjusting the drawtube to the prcper length as determined by actual 
measurement of the field, a 16 mm Zeiss apochromatic objective with a Zeiss X6 
compensating ocular or a Spencer 16 mm apochromatic objective with a Spencer 
X10 compensating ocular, or their equivalents, being used to obtain the proper 
magnification. 
1 These numbers refer to the sections as given in the Journal of the Association of Official Chemists, 
November, 1916. 
2Comment by authors: In using these celis the plane parallel cover glasses furnished with them by 
maker should be used instead of the ordinary microscope cover glasses, since the latter are subject to 
curvatures that introduce errors in the thickness of the mounts. 
3 Comment by authors: In order to have an area of 1.5 sq. mm the diameter of the microscopic field 
should be 1.382 mm. This is determined by using a stage micron eter and adjusting the length of the 
microscope drawtube. Obviously after the proper drawtube length has been secured that adjustment. 
shculd be noted and always used in making mold counts. 
