324 MERCURY. 



irritation which they are liable to occasion. Hence, this com- 

 bination is peculiarly useful where it is difficult to cause purging, 

 or where, from the state of the stomach, the usual cathartics are 

 liable to be rejected, especially when they are given in large doses. 

 The dose, as a cathartic, is from five to ten or even fifteen grains. 

 When prescribed with other intentions, the dose is various ; as an 

 alterative a grain is given night and morning, and this, after being 

 continued for some time, will affect the system. When it is 

 necessary that this should be done more speedily, a large dose is 

 prescribed, and, if necessary, its purgative operation may be 

 obviated by opium."* Calomel and lime-water forms what is 

 commonly termed the black lotion, so much employed by sur- 

 geons as a soothing application to venereal sores and excoriations. 



Bl-CHLORIDE OF MERCURY, OR CORROSIVE SUBLIMATE. 



Hydrargyri Oxymurias. Ph. L. — Bi- chloride of Mercury is 

 prepared for medicinal purposes by boiling two pounds of mer- 

 cury with two and a half pounds of sulphuric acid to dryness, in a 

 glass vessel, then mixing the dry mass with four pounds of chloride 

 of sodium (common salt), and subliming. When thus obtained, 

 it is of a crystaline texture, colourless, and semi-transparent. It 

 has a very disagreeable, styptic, and somewhat acrid, metallic 

 taste. Its specific gravity is 7 2. ■ It is soluble in 20 parts of 

 water at the temperature of 60°, and 2 of boiling water ; it is 

 also soluble in alcohol, and requires little more than three 

 parts of that fluid for its solution. Muriate of ammonia con- 

 siderably increases its solubility, one part rendering five parts 

 soluble in about five of water. It dissolves readily in muriatic- 

 acid, but is insoluble in concentrated nitric and sulphuric acids. 

 The fixed alkalies and alkaline earths decompose it, precipitating 

 it from its solution of an orange-yellow colour, which becomes 

 brick-red. It is also decomposed by many metals, compound 

 salts, and vegetable infusions. In this preparation, as the name 

 implies, the mercury is combined with one proportional of metal 

 and two of chlorine. The bi-chloride, or proto-chloride of mer- 

 cury, as it is also called, is the most active of all the preparations 



* Murray's System "/Materia Medica, v. i., p. '208. 



