81 



In the presence of both caleiuni sulphate and calcium carbonate 

 added in excess to a solution of magnesium sulphate, the limit of 

 endurance is only two-thirds as liigh as when calcium sulj^hate alone 

 is added. 



Calcium as the chloride has also a powerful effect in neutralizing the 

 toxicity of magnesium suli>hate. But h^re the addition of a new 

 anion (CI), besides the added cathion (Ca), seems to diminish the 

 beneficial effect of the latter, since the chloride, although a readily 

 soluble salt, raises the limit for magnesium sulphate only one-third as 

 much as does the little- soluble calcium sulphate. In a mixture of 

 calcium chloride and magnesium sulphate a crystalline precipitate of 

 calcium suli:)hate separates slowly or rapidly in i^roportion to the con- 

 centration of the solutions, so that the case becomes that of the 

 contact of solid calcium sulphate with a' solution of magnesium chlo- 

 ride. As would be expected, the limit of endurance for magnesium 

 sulphate j^lus calcium chloride is the same as that for magnesium 

 chloride plus calcium sulphate (Table V). 



Sodium salts are very much less effective in neutralizing magnesium 

 sulphate than are salts of calcium. In the case of sodium salts it is 

 the chloride which is most effective, so that here we seem to have a 

 beneficial effect of the anion as well as of the cathion. Yet the absence 

 of any neutralizing effect when magnesium chloride is added to mag- 

 nesium sulphate shows that the CI ions alone are ineffective. 



In one case the addition of a salt with a common basic ion — i. e., 

 magnesium carbonate — raises the limit of endurance in magnesium 

 sulphate eight times. ^ By a simple process of elimination, since 

 magnesium ions are ineffective in the form of magnesium chloride 

 when added to magnesium sulphate, although chlorine ions appear 

 to have in themselves some neutralizing value when added as sodium 

 chloride, we are compelled to attribute the beneficial influence of 

 magnesium carbonate to CO3, or more iDrobabh' HCO3, ions, a point to 

 which we will return in discussing the stimulating effect of dilute 

 solutions of sodium carbonate and sodium bicarbonate. Noteworthy 

 is the fact that calcium carbonate, although much less soluble than 

 the corresponding salt of magnesium, is twice as effective an anti- 

 dote for magnesium sulphate. This affords another striking proof of 

 the great efficacy of calcium as a remedy for magnesium poisoning. 



solntion), is the isotonic equivalent of a 0.1 normal solution of potassium nitrate, 

 which is usually taken as the unit in measurements of osmotic pressure of solu- 

 tions. True [Hot. Gazette, 26, p. 410 (1896)] found that plasm olysis of Spirogvral 

 cells in a KNO, solution first appeared at a concentration of O.'2o normal. De 

 Vries* results seem to indicate that the osmotic value of each component in a 

 mixed solution (of two or three salts) is equal to that of the respective compo-. 

 nent when present alone at the given concentration, a point not in accord with 

 well-established facts. 



'The roots barely sui-vive in poor condition in a 0.01 normal magnesium sul- 

 phate solution plus an excess of magnesium carbonate: but in O.OOo normal magne- 

 sium sulphate solution plus magnesium carbonate some of the roots were perfectly 

 normal after a twentv-four hours' culture. 



