The Absorption Coefficient of Solution for Monochromatic Radiation. 17 

 ERRORS AND CORRECTIONS. 



The values of a and of A have been plotted against wave-length and 

 concentration respectively. It was thought better to connect the 

 plotted points by straight lines rather than to draw smooth curves 

 through them. A glance at the figures shows that the absorption 

 curves i. e., the curves of a against wave-length are fairly smooth, but 

 that the curves of A against c are quite irregular. The inaccuracy in 

 the values of A, as shown by the irregularities in the curves, is quite 

 large. In many cases the deviations of the broken line indicate as 

 much as 10 per cent variations in A. The causes of such errors are 

 many. Without going into tedious and obvious details, it is only 

 necessary to state that the accurate determination of a depended upon 

 the proper choice of cell depth, which was regulated by the actual value 

 of the absorption coefficient, as well as upon the care used in preparing 

 the solutions and in cleaning and adjusting the cells. Errors also 

 resulted from the poor keeping qualities of certain solutions. The 

 deflections of the radiomicrometer could be duplicated to within a milli- 

 meter. Hence the ratio of the deflections for each cell was usually 

 accurate to within 2 per cent. In cases where the absorption coefficient 

 was large, the deflection for the thick cell was small and the error pro- 

 portionately greater. The values of a in the tables are considered to 

 be accurate to within 3 per cent, the error being greater for very high 

 and very low values of a. A was calculated from formula (2) and devi- 

 ations of 5 to 10 per cent were within the error of experiment. The 

 chance for error in A was much greater for the dilute solutions than 

 for the more concentrated ones, so that it was the practice to make 

 up the solutions below a concentration c = l in smaller steps than in 

 the case of solutions for which c was greater than 1. The calculations 

 of a and A have been carried out to three figures in most cases, although 

 quite often the third figure is not significant. 



The concentration c is defined to be the number of gram-molecules 

 of salt per liter of solution, and the solutions were prepared in con- 

 formity with this. The calculation for A, however, has been made 

 on the basis that c is the concentration in gram-molecules of salt per 

 liter of solvent. 



The procedure of calculating A by formula (2) presupposes that 

 in 1 mm. layer of solution there is a 1 mm. layer of solvent plus the 

 dissolved salt. This, however, is not strictly true, because the addition 

 of the salt to the solvent produces sometimes expansion and some- 

 times contraction. The error in the value of A due to this is, how- 

 ever, negligible in comparison with the errors arising in other ways. 

 For example, consider the case of an aqueous solution of CoC^, when 

 c = 1.90. At wave-length 979ju/x, a = 0.0742. Assuming no expansion 

 upon dissolving, 



