DUBOSCQ COLORIMETER 147 



other (or within about 20 per cent if the readings are made at 

 depths as great as 50 to 60 mm.) accurate results may, however, 

 be obtained directly. If the variations are greater than this a 

 correction is necessary. Kober has proposed an equation to supply 

 this correction and thus make possible very accurate work under 

 conditions of moderate variations of concentration. The equation 

 is as follows: 



_ s (1 x)sk 

 y ~'x~ ~^~ 

 or 



_s+s/b+ v (s+sfc) 2 4sky 



Ju ~ 



where y = height of unknown solution, on the left side of the 

 instrument, when standard solution is kept on the right side at 

 a definite height, s = height of standard solution on the left side 

 and x = the ratio of the concentrations of the two solutions. 



Tf 



k = , where K = a constant, obtained by substitution of 

 s 



standardization values of s, y, and x. The instrument should 

 be checked up for each series of analyses by reading the standard 

 against itself and determining the potential height of the standard 

 solution by reading the scale on the left side when the solution 

 on the right side is kept at a definite height, and the two are 

 matched. 



DUBOSCQ COLORIMETER TRANSFORMED 

 INTO A NEPHELOMETER 



(Bloor) ! 



The following description for changing the Duboscq colorimeter 

 into a nephelometer applies only to the later type of colorimeter, 

 that is, the cups move and the prisms are stationary. The extra 

 parts necessary are supplied in an improved form by the Inter- 

 national Equipment Company of Cambridge, Mass. By the use 

 of these parts the change may be quickly made as follows : 2 

 Unscrew the movable glass prisms of the colorimeter, slip the 



1 Bloor: Jour. Biol. Chem., 1915, 22, 145. 



2 Folin: A Laboratory Manual of Biological Chemistry, 1919 



