OF CERTAIN ORGANIC ACIDS IN AQUEOUS SOLUTIONS. 53 



The method of preparing the solutions was that devised by West 

 and Jones: 



"Since we worked over a range of temperature of only 30, we found it 

 convenient to prepare the solutions at the intermediate temperature, 50, and 

 then to use the solutions at the three temperatures, 35, 50, and 65. But 

 since the volume of a solution varies with the temperature, it was, of course, 

 necessary to apply a correction at 35 and 65 to the volume of solutions 

 made up to 50. 



"When a standard solution is cooled from 50 to 35 there is a contraction 

 in volume and a consequent increase in the concentration of the solution. 

 The value of /* for any solution would, therefore, be slightly too large. The 

 value of fj. v as found must be multiplied by the factor 0.994 for results at 35 

 when the solutions were made up at 50. The correction factor for solutions 

 made up at 50 and used at 65 is 1.0076. The coefficient of expansion for 

 distilled water is somewhat less than that for an aqueous solution. However, 

 the difference in the coefficients for water and for that of our most concentrated 

 solution is so small that it is negligible. By making use of the above correction 

 it was necessary to prepare only one set of solutions for each salt; and, conse- 

 quently, much pure material and time were saved." 



When Wightman, Springer, and Smith began the investigations at the 

 higher temperatures the two problems presenting themselves were : 



(1) In making up the solutions at 50 the glass of the flasks would 

 dissolve, because the flasks were not kept at 50 in a bath, but, when 

 not in use, were allowed to cool down to room temperature. 



(2) The solution, even if heated to 50, would cool off when poured 

 into the burette, and still further when draining into the flask; there- 

 fore, instead of drawing off 50 c.c. of the solution at 50, 50 c.c. would 

 be drawn off at a temperature of 50 x, or more than 50 c.c. at 50. 



This complex source of error was overcome by the above-named 

 workers, all of whom started simultaneously the present line of work 

 at elevated temperatures. The results are given in the paper by 

 Springer and Jones: 1 



o 



"A simple device did away with both of these sources of error. At 50 

 988.07 grams of distilled water have a volume of 1000 c.c. Our liter flask 

 was weighed at 20. Then 988.07 grams of distilled water at 20 were intro- 

 duced air displacement being taken into account. The flask was marked at 

 the bottom of the meniscus. This flask, filled to the mark with water at 20 

 (room temperature), will contain a liter at 50. Therefore, all the mother 

 solutions could be made up for 50 work at 20, and the solubility of the glass, 

 which is noticeable only at higher temperatures, is thus made negligible. This 

 mother solution will be, let us say, normal at 50. At 20 it is stronger than 

 normal. If we draw out 100 c.c. at 20 and dilute it to 200 c.c. at 20, it will 

 also be stronger than half-normal. But heat this latter solution to 50 and it 

 will again attain its required normality assuming that the coefficient of 

 expansion of water is the same as that of dilute solutions. And all solutions 

 worked with were eighth-normal, or more dilute. This permits the titration 

 of all solutions at room temperature, which obviates the second of the above 

 difficulties." 



. Chem. Journ.. 48, 417 (1912). 



