effects which may be occasionally produced by the external application of lead, since the fact has been questioned, and is still considered by many as involved in doubt and uncertainty. _Dr. Lambe_ is inclined to believe, that “to the production of the saturnine colic, it is necessary that the metal should be applied _immediately_ to the stomach and intestines.” If this hypothesis be just, he excludes nervous sympathy, as well as absorption, as a proximate cause of saturnine colic; and, consequently, no dependence can be placed on the accounts given by the above pathologists with regard to the production of such an effect by lotions and cataplasms of lead. _Of the chemical processes, by which the presence of lead may be detected._ These will necessarily vary according to the different states of combination in which it may be supposed to exist; we shall, therefore, proceed to consider the modes of establishing its presence, 1, In solution in _water_; _wine_; _spirit_; and _oils_. 2. In a state of mixture with _various solids_. 3. Combined with _solid or liquid aliments_. 1. _The lead exists in some unknown state of combination in solution in water._ We are greatly indebted to _Dr. Lambe_[390] for the able directions which he has afforded us for ascertaining the presence of minute portions of lead in water; and we recommend the practitioner, who may be engaged in such an investigation, to peruse his work with attention. The following are the reagents through which our analysis must be conducted. (_a_) _Sulphuretted hydrogen._ A solution of this gas in distilled water is a very delicate test for lead, throwing down a precipitate of a very dark brown colour, approaching to black. The competency, however, of this test to the discovery of very minute quantities of lead, in certain states of combination, has been questioned by _Dr. Lambe_; who was enabled to detect the presence of this metal, by other methods, in water that manifested no indication with _sulphuretted hydrogen_. He detected it, for instance, in the precipitate occasioned in such water by the carbonate of potass or soda. In operating on these waters, he noticed the following appearances. 1. _The precipitate, produced as above stated, when re-dissolved in nitric acid, formed a dark cloud with sulphuretted hydrogen._ 2. _Although the sulphuretted hydrogen formed no cloud, the precipitate itself became darkened by it._ 3. _The precipitate re-dissolved in nitric acid_, (as in 1) _formed, with sulphuretted hydrogen, a white cloud._ 4. _Sulphuretted hydrogen neither formed a cloud, nor darkened the precipitate._