2Q4 PHYSIOLOGICAL CHEMISTRY 



continuous use as a nephelometer. If the change is desired the nephe- 

 lometer tubes are to be supported in the same way as above, but the 

 jackets must be carried on special brackets which are made to replace 

 the brackets carrying the plungers. The nephelometer tubes must be 

 stationary, the jackets being the movable parts. 



Kober has devised 1 a combined colorimeter and nephelometer less 

 expensive than the Duboscq apparatus and which may be obtained 

 in this country. 2 A diagram illustrating the construction of this 

 Lenzmann-Kober nephelometer is given in Fig. 85, page 293. 



N ephelometric Calculations. The amounts of precipitate in solu- 

 tions examined nephelometrically is not exactly inversely proportional 

 to the readings of the scale. When the concentration of the unknown 

 and of the standard are within 10 per cent of each other (or within 

 about 20 per cent if the readings are made at depths as great as 50- 

 60 mm.) accurate results may however be obtained directly. If the 

 variations are greater than this a correction is necessary. Kober 3 

 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: 



x)sk 



_ 



y= x~ 



or 



2y 



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

 ment, 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. 



T 



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

 5 



zation 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. 



i. Acetone Bodies. N ephelometric Methods of Marriott. 4 Prin- 

 ciple. Acetone in very small amounts forms a cloudy solution with the 

 Scott- Wilson reagent which may be read nephelometrically. By this 



1 Kober: Jour. Ind. and Eng. Chem., 7, 843, 1915. 



2 The instrument is manufactured by Lenz and Naumann Pullman Building, 17 Madison 

 Ave., New York City. 



3 Kober: /. Am. Chem. Soc., 37, 2379, 1915; Jour. Biol. Chem., 13, 485, 1913. 



4 Marriott: Jour. Biol. Chem., 16, 289 and 293, 1913. 



