POTASSIUM AND ITS MEDICINAL COMPOUNDS 173 



seen to be on the central nervous system. The spinal cord 

 is markedly stimulated, reflex irritability is increased, and 

 tetanic convulsions may be caused. Blood pressure rises 

 and respiration becomes accelerated, whilst the heart may 

 be slowed from stimulation of the vagus (inhibitory centre). 

 With excessive doses paralysis of the central nervous system 

 results, and the animal dies of asphyxia. Given by the 

 mouth ammonium salts are more readily absorbed than the 

 same salts of potassium or sodium, but they do not become 

 sufficiently concentrated in the blood to cause convulsions, 

 or even marked effects on the central nervous system. 

 Moreover, the mucous membrane of the lungs is impermeable 

 to ammonium, so that ammonia vapour inhaled only affects 

 the nervous system reflexly through its local action. 



In their primary stimulation and secondary paresis, 

 ammonium salts resemble the mono-hydric alcohols and 

 ethers ; but they act more markedly on the cord and motor 

 centres, and less on the higher cerebral centres. Ammonium 

 salts increase the secretion of the bronchial and intestinal 

 glands, and also of the sweat glands and kidneys, <by which 

 they are mainly excreted. In the blood of mammals 

 ammonia is converted almost entirely into urea, in the blood 

 of birds into uric acid. 



POTASSIUM AND ITS MEDICINAL COMPOUNDS 



Potassium salts are obtained from (1) carnallite, a chloride 

 of potassium and magnesium (KCl.MgCl 2 .6H 2 O) overlying 

 the rock-salt in the mines of Stassfurt in Saxony ; (2) from 

 the crude potashes got from wood ashes ; and (3) from the 

 argol deposited during the fermentation of wine (p. 188). 

 Most are soluble in water. They are identified in solution 

 by their negative reaction with the several group tests for 

 the metals, while moderately strong neutral solutions rather 

 slowly form, with sodium hydrogen tartrate, a white crystal- 

 line precipitate (KHC 4 H 4 6 ), soluble in hydrochloric acid 

 and in caustic potash. Evaporated to dryness, and ignited 

 with alcohol, they produce a distinctive violet-coloured 

 flame, which gives on the spectrum two lines one intense 

 on the red, the other transient on the violet. 



