214 PURGATIVE, ALTERATIVE, AND FEBRIFUGE 



sea-water, and in some mineral springs. It derives its ver- 

 nacular name from the mineral springs of Epsom. It may 

 be prepared by the interaction of the native magnesium 

 carbonate and diluted sulphuric acid ; or by purifying the 

 native sulphate (B.P.). 



PROPERTIES. Epsom salt occurs in transparent, colour- 

 less, minute, rhombic prisms. It has a cooling, saline, 

 nauseous, bitter taste ; is insoluble in alcohol, but soluble in 

 its own weight of water. It resembles zinc sulphate, from 

 which, however, it is distinguished by its saline, bitter taste, 

 by absence of metallic astringency, and by its neutral solu- 

 tion giving no precipitate with hydrogen sulphide. Epsom 

 salt is distinguished from Glauber salt by its neither effloresc- 

 ing when exposed to air, nor communicating any yellow 

 colour to the flame of alcohol. From oxalic acid (for which 

 it has been sometimes mistaken) it is distinguished by its 

 finer and more needle-like crystals, its bitter taste, devoid of 

 acidity, and its precipitating alkaline carbonates without 

 effervescence. 



ACTIONS AND USES. Epsom salt is purgative, alterative, 

 and febrifuge, and is also feebly diuretic and diaphoretic. 

 As a purgative it resembles common and Glauber salts, and 

 is more active than potassium bitartrate or sodium phos- 

 phate. 



GENERAL ACTIONS. When swallowed, it causes outpour- 

 ing of fluid from the walls of the small intestines, most 

 quickly produced, and abundant when the bowels have been 

 partially emptied by several hours' fasting. Neither pan- 

 creatic fluid nor bile is materially increased. But Epsom 

 salt, like other salts in solution, becomes dissociated into its 

 basic and acid ions, namely Mg and S0 4 , and experiment 

 shows that both these penetrate the intestinal mucous 

 membrane very slowly and with difficulty. As a conse- 

 quence, when a strong solution (hypertonic) of magnesium 

 sulphate is introduced into the intestine the salt remains 

 there, both ions exerting their osmotic pressure and drawing 

 fluid from the blood to dilute the solution in the bowel. 

 Thus by the osmotic action of magnesium sulphate the 

 fluid contents of the bowels are increased, producing more or 

 less mechanical distension, and provoking, like other salines, 



