102 PROCEEDINGS OF SECTION B. 



decolourized. This lies between the last decolourized flask and the next 

 in the series which retains its pinkness. A reserved 100 c.c. sample 

 can finally be tested with half a c.c. more standard solution than was 

 required by the decolourized flask. A correction for actual volume 

 in the 100 c.c. flask is made, subtracting, of course, the volume of 

 standard solution added. 



It remains but to add that ordinary care will have to be exercised 

 in protecting the standard solution from the natural action of the air 

 surrounding it. This can be done in the burette by the aid of a soda- 

 lime filter, the burette being preferably large enough for the whole set 

 of experiments. The solution may also be conveniently kept in an 

 ordinary separator similarly protected. I do not find, however, that 

 using reasonable expedition in pouring the solution into the burette 

 and in running it into the flasks there is any appreciable alteration 

 in its strength. 



7.— THE EFFECT OF NEUTRAL SALTS ON THE SOLUBILITY 

 OF ORTHO-PHTHALIC ACID. 



By A. G. D. Rivett, B.A., B.Sc, and E. I. Rosenblum, M.Sc. 



(Abstract.) 



The authors aimed at an extensive examination of the effects of 

 salts on the solubility of o-phthalic acid. In the considerable number 

 of previous researches on similar lines, dealing with gaseous, solid, 

 or liquid solutes, workers have seldom made their selection of salts 

 extensive enough for purposes of comparison. The list examined in 

 the present case includes the chlorides of the following positive radicles, 

 viz., lithium, sodium, potassium, rubidium, caesium, ammonium, 

 hydrogen, magnesium, calcium, and barium ; the potassium salts of 

 the following negative radicles, viz., chloride, bromide, iodide, fluoride, 

 chlorate, bromate, iodate, nitrate, sulphate, and acetate ; the nitrate 

 and sulphate of sodium ; and also acetic acid, mercuric cyanide, ethyl 

 alcohol, and cane sugar (pure and partly inverted). Temperatures 

 worked at were 25" and 35° C. All salt concentrations were expressed 

 in gramme-molecules per litre, but densities were determined for all 

 solutions, so that the mode of representing concentration might be 

 changed if necessary. It was pointed out that in view of the difficulty 

 in finding a satisfactory method for the calculation of concentration, 

 it was desirable that all workers on solutions should determine the 

 densities of the solutions they examine, so as to make their work avail- 

 able for re-calculation later should a different mode of expressing con- 

 centration seem desirable. 



The general form of curve representing relative solubility of the 

 phthalic acid against salt concentration shows an initial rise followed 



