INTRODUCTION 5 



made much more accurate by uniform methods of technique, 

 aided by certain mechanical devices. For example, in the ex- 

 amination of vegetable powders, spices, meals, flours and similar 

 substances, the samples should be thoroughly mixed, and slide 

 mounts should be of standard and uniform thickness and the 

 relative amounts of the ingredients should be estimated by means 

 of microscope slides having uniform ruled squares of definite 

 measuring value in microns. These and other details in the 

 methods should be more fully worked out. 



Several micro-analysts have declared themselves as opposed 

 to giving percentage estimates of the several ingredients of a 

 compound. However, not to give the approximate percentages 

 will cause great confusion and very materially lessen the value of 

 the work done. For example, to report a pancake flour as com- 

 posed of "buckwheat and wheat flour, the former predominating," 

 instead of "buckwheat approximately 75 per cent, and wheat 

 approximately 25 per cent.," would certainly be unsatisfactory. 



The following examples will serve to explain the relative value 

 of the chemical and microscopical analyses. Suppose the sub- 

 stance to be examined is a baby food. The microscope may re- 

 veal approximate percentages of oil globules, steam dextrinized 

 wheat starch, unchanged wheat and arrowroot starch, wheat 

 tissue and milk sugar. The chemical analysis will show a definite 

 percentage of sugar, soluble starch, insoluble starch, fat, vege- 

 table fiber and ash. This is a good example of a case where the 

 two methods of analysis are of equal importance; one without 

 the other would be unsatisfactory, incomplete and inconclusive. 

 Again, the chemical assay may show that a sample of powdered 

 belladonna leaf contains 0.35 per cent, of mydriatic alkaloids, and 

 yet the microscopical examinations may prove the presence of 

 20 per cent, or more of some foreign leaf. 



An adjunct in analytical work, much neglected by the chemist, 

 is the organoleptic testing. This is especially important in 

 the examination of unknown substances, fruit products, spices, 



