This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Dreshler recommends: Add three drops of one part bichromate of potassium in ten parts nitric acid of 1.30 to five drops of the suspected oil. Coloration if alcohol be present.
For detecting chloroform in essential oils Hager recommends to add fifteen drops of the suspected oil to from fifty to sixty drops of alcohol and thirty drops of diluted sulphuric acid (strength ten percent on the hydrometer or acidometer), shaking well, and heating with a few pieces of zinc. After twenty minutes (or when all evolution of hydrogen has ceased) add an equal volume of cold water, shake, and run through a wet filter. Acidify strongly with nitric acid, and add a solution of nitrate of silver. A precipitate of chloride of silver will appear if chloroform was present. When, besides chloroform, hydrocyanic acid is present, as may be the case in oil of bitter almond, treat on cyanide of silver. (See test for oil of bitter almond.)
A. W. Hoffmann's test is considered the best. In an alcoholic solution of soda hydrate, pour some of the suspected oil and add a fraction of aniline, heating gently. When even the smallest quantity of chloroform is present, the disagreeable and stunning odor of nitriles is at once perceptible.