164 Proreedhigfi of Indiana Academy of Science 



ConduHiuuH. From the statements already made concerning the 

 several variable factors involved in this work, one would predict cer- 

 tain of the results that are apparent in tables 1 and 2. The rate of 

 evaporation should be greater in the 100 ml. burettes than in those of less 

 capacity having a shorter radius of exposed surface; it should be less 

 for water than for benzene which has, for a given temperature, a higher 

 vapor tension; the vapor pressure of a solution 5N is less than that 

 for one 0.25N, hence the rate should be less for the more concen- 

 trated solution; and covers over the ends of the burettes should de- 

 crease the rate, due to their partial closing cf the systems and con- 

 sequent prevention of freely circulating air from carrying away the 

 gaseous molecules of the liquids. 



On account of the rather complex situation prevailing in these 

 experiments, with the several variable factors uncontrolled, it is not 

 possible to point out the effect of each variation. It seems probable that 

 the effects of changes in bare metric pressure and relative humidity are 

 relatively small as compared with that for changes in temperature. An 

 inspection of the results in table 2 for the eighth and ninth days shows 

 a small change of the former variables but a distinct increase in the 

 leadings of the burettes, even though a decrease in the temperature 

 should have decreased the vapor tension of the water and thus have 

 decreased the rate of evaporation. It seems evident that a change of 

 temperature of the solutions produces a change of volume considerably 

 larger than the change resulting from a change of vapor tension, and in 

 the opposite direction. 



It has already been stated that experiments conducted under the 

 conditions prevailing during this work cannot give entirely satisfactory 

 results, but they do furnish a general basis for predicting what may 

 happen when such measurements are made in the usual laboratory. It 

 is evident that caps on burettes do retard the rate of evaporation; but 

 it is also evident that the total loss through evaporation for an aqueous 

 solution is .small at the end of a day, even in the open burettes, and one 

 never takes such a length of time for the ordinary titration. Changes 

 of temperature are liable to cause a much greater change in the volume 

 of a standard solution. 



THE USE OF SOLUTIONS OF INORGANIC SALTS AS 

 PERMANENT COLOR STANDARDS. 



M. G. Mellon, Purdue University. 



In the colorimetric determination of certain substances a common 

 procedure consists in comparing, by means of a colorimeter or some 

 other device suitable for the desired accuracy, a definite volume of a 

 solution containing the unknown substance with various standard solu- 

 tions containing definite amounts either of the constituent being deter- 

 mined, or of some other substance showing the same color as this con- 

 stituent. When a match is found between the unknown and one of the 

 standards, it is assumed that the amounts of the color-forming constitu- 



