Note 4 — Chapter I

Potassio-mercuric iodide, made by dissolving 50 grammes of potassium iodide and 13·5 grammes of mercuric chloride, in a litre of distilled water. The reagent is added till no further precipitate is produced, which is known by filtering a small portion at intervals and testing with the potassio-mercuric iodide to see if finished. The strength of the solution must be, as nearly as possible, 1 part of the alkaloid in 200, so that an approximate idea must first be obtained by weighing or otherwise. As the quantity is in poison cases generally too small to weigh, the approximate idea must be gathered by comparing the intensity of the tests with those furnished by known amounts of the alkaloid. Each cubic centimetre of Mayer’s solution precipitates ·02 gramme of morphia, ·0268 of aconitia, and ·0167 of strychnia. For further details see Blyth’s Practical Chemistry, 1879, p. 289.