If the substance be of an organic nature, a peculiar empyreumatic odor will be given off.  If the substance chars, then it may be inferred that it is of an organic nature.  The matters which are given off and cause the empyreumatic odor, are a peculiar oil, ammonia, carbonic acid, acetic acid, water, cyanogen, and frequently other compounds.  If a piece of paper is heated in the bulb, a dark colored oil condenses upon the sides of the tube, which has a strong empyreumatic odor.  A piece of litmus paper indicates that this oil is acid, as it is quickly changed to red by contact with it.  A black residue is now left in the tube, and upon examination we will find that it is charcoal.  If, instead of the paper, a piece of animal substance is placed in the bulb, the reddened litmus paper will be converted into its original blue color, while charcoal will be left at the bottom of the tube.

A changing of the substance, however, to a dark color, should not be accepted as an invariable indication of charcoal, as some inorganic bodies thus change color, but the dark substance will not be likely to be mistaken for charcoal.  By igniting the suspected substance with nitrate of potassa, it can quickly be ascertained whether it is organic or not, for if the latter, the vivid deflagration will indicate it.

If the substance contains water, it will condense upon the cold portion of the tube, and may be there examined as to whether it is acid or alkaline.  If the former, the matter under examination is, perhaps, vegetable; if the latter, it is of an animal nature.  The water may be that fluid absorbed, or it may form a portion of its constitution,

If the substance contain sulphur, the sublimate upon the cold part of the tube may be recognized by its characteristic appearance, especially if the substance should be a sulphide of tin, copper, antimony, or iron.  The hyposulphites, and several other sulphides, also give off sulphur when heated.  The volatile metals, mercury and arsenic, will, however, sublime without undergoing decomposition.  As the sulphide of arsenic may be mistaken, from its color and appearance, for sulphur, it must be examined especially for the purpose of determining that point.

Selenium will likewise sublime by heat as does sulphur.  This is the case if selenides are present.  Selenium gives off the smell of decayed horse-radish.

When the persalts are heated they are reduced to protosalts, with the elimination of a part of their acid.  This will be indicated by the blue litmus paper.

If some of the neutral salts containing a volatile acid be present, they will become decomposed.  For instance, the red nitrous acid water of the nitrates will indicate the decomposition of the salt, especially if it be the nitrate of a metallic oxide.

If there is an odor of sulphur, then it is quite probable, if no free sulphur be present, that a hyposulphite is decomposed.