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ILLINOIS BIOLOGICAL MONOGRAPHS 



[176 



determined. All concentrations used must fall within the range of concen- 

 trations where the velocity of fataUty curve approaches a straight line. (Con- 

 centrations represented from A to B, curve CABG, Fig. 1). A graph should 

 then be dravvTi with reciprocal of survival time as ordinate and the ratio of the 

 substance used as abscissa (i.e., the theoretical velocity of fatality curve) on 

 some standard scale. This curve which is practically a straight line and should 

 be drawn as a straight line should then be compared to a standard curve which 

 has been previously prepared from experimental data of the same substance at 

 the same temperature or a curve d^a^vn from data of experiments testing a 

 known solution or standard of the same substance where a standard solution is 

 available. The latter eliminates any error due to seasonal variation, variation 

 in stock of goldfish, physiological state of the goldfish as well as variations in 

 temperature at which the experiments can be rim. Then the strengths of 

 the known and the luiknown solutions are inversely proportional to the dis- 

 tances from the origin O at which their theoretical velocity of fatality curves 

 cut the X-axis. That is, the strength of the unknown solution is to the strength 

 of the known solution as the distance from the origin O to the point where the 

 theoretical velocity of fatality curve of the known solution cuts the X-axis 

 is to the distance from the origin O to the point where the theoretical velocity 

 of fatality curve of the unknown solution cuts the X-axis. For example, let 

 e = strength of the known solution represented by the theoretical velocity of 

 fatality curve SMP, Fig. 24, t'= strength of an unknown solution No. 1, repre- 

 sented by the theoretical velocity of fatahty curve SP'M', and M=the strength 

 of an imknown solution No. 2, represented by the theoretical velocity of fatality 



1 11 111 



curve SP"M." Then v:e:u= — :-=-:-^ = . . 



OP' OP OP" b a c 



where a = distance 



100 



t 



40. 60. 80. 100. 120. 140. 160. 180. 200cc. 



Figure 24. Lithium chloride. Graphs showing method of determining the normality 

 of an imknown LiCl solution. 



SPM = Theoretical velocity of fatality curve of a known solution of LiCl 



SP'M' = 

 SP"M"= 



" " an xmknown 

 » » » » 



" No. 1 

 » » 2 



