§ 116. The neutral salts of the alkalies are poisonous, if administered in sufficient doses, and the poisonous effect of the sulphate, chloride, bromide, iodide, tartrate, and citrate appears to depend on the specific action of the alkali metal, rather than on the acid, or halogen in combination. According to the researches of Dr. Ringer and Dr. Harrington Sainsbury,[126] with regard to the relative toxicity of the three, as shown by their effect on the heart of a frog--first, the potassium salts were found to exert the most poisonous action, next come the ammonium, and, lastly, the sodium salts. The highest estimate would be that sodium salts are only one-tenth as poisonous as those of ammonium or potassium; the lowest, that the sodium salts are one-fifth: although the experiments mainly throw light upon the action of the alkalies on one organ only, yet the indications obtained probably hold good for the organism as a whole, and are pretty well borne out by clinical experience. [126] _Lancet_, June 24, 1882. There appear to be four cases on record of poisoning by the above neutral salts; none of them belong to recent times, but lie between the years 1837-1856. Hence, the main knowledge which we possess of the poisonous action of the potassium salts is derived from experiments on animals. § 117. =Sodium Salts.=--Common salt in such enormous quantity as half a pound to a pound has destroyed human life, but these cases are so exceptional that the poisonous action of sodium salts is of scientific rather than practical interest. § 118. =Potassium Salts.=--Leaving for future consideration the nitrate and the chlorate of potassium, potassic sulphate and tartrate are substances which have destroyed human life. =Potassic Sulphate= (K₂SO₄) is in the form of colourless rhombic crystals, of bitter saline taste. It is soluble in 10 parts of water. =Hydropotassic Tartrate= (KHC₄H₄O₆), when pure, is in the form of rhombic crystals, tasting feebly acid. It is soluble in 210 parts of water at 17°. § 119. =Action on the Frog’s Heart.=--Both excitability and contractility are affected to a powerful degree. There is a remarkable slowing of the pulsations, irregularity, and, lastly, cessation of pulsation altogether.