This section is from the book "The Steward's Handbook And Guide To Party Catering", by Jessup Whitehead. Also available from Amazon: Larousse Gastronomique.
The government chemists, investigating the adulterations of food, say: "These spices are the barks of several species of the geniis cinnamonum, the true cinnamon being a native of Ceylon, where it is largely cultivated, and the cassias being derived from several other species growing in China, India and the East Indies. Cinnamon as it reaches the market is very thin, the outer and inner coats of the bark having been removed. Cassia, on the other hand, is thick, as it consists of the entire bark, and can be distinguished by its retaining its natural outer surface. Cinnamon is by far more valuable than the cassia, as there is a smaller supply and intrinsically it contains a much greater proportion of volatile oil, and that of higher and more delicate aroma. In consequence cassia is largely substituted for cinnamon, and, in fact, not a particle of ground cinnamon can be found in the market. It can be found in the whole condition in good quality only in drugstores. Cassia exists in many forms and qualities, and sells at wholesale at from 7 to 40 cents a pound. That known as Saigon is the best and that exported from Batavia the poorest.
Cassia buds also hold a small place in the market The detection of the substitution of cassia for cinnamon, since the barks are of trees of the same species, is more difficult than is usually the case and may prove troublesome to a novice. The presence of more woody fiber in the latter with the aid of chemical analysis serves, however, as a reliable distinction. In the samples which have come into our hands not a particle of material labeled ground cinnamon proved to be anything other than cassia. The spice millers appeared however, to be satisfied to stop at this point and in only one case was there addition of cheap stuff to the cassia. When added there is no difficulty in detecting it as has been done here and in Canada where peas, starch, ground shells and crackers have been found in powder labeled both cassia and cinnamon. The barks can, in most cases, and especially the cinnamon, be used nearly as well in the whole condition, and should at least be so purchased and then ground. A slight acquaintance with the appearance of the different qualities will teach one the proper selection to make".