REFRACTOMETRIC APPLICATIONS 



related to their acid value and their iodine this method (144). Some attempts at detect- 



number, and it is a sensitive index of mild ing antihormones by refractometry (145) 



oxidation. should be mentioned. The study of isotope 



Criminological applications have been de- exchanges in biological systems was cursorily 



tailed by Kirk (131). Empirical methods of tried by the writer (146) in 1939. A contem- 



analysis based on refractometry may be de- porary renewal of interest in this field is 



veloped on a purely experimental basis. For manifest (147). 



instance, chemical titrations of weak poly- Still another fruitful field of investigation 

 electrolytes, in dilute nonaqueous solutions is the study of binding power of proteins 

 without indicator, are possible with unam- and of other products of biological and medi- 

 biguous end points. The method is often cal interest. It seems that the refraction in- 

 more sensitve than high-frequency titrimetry crement of blood proteins can be markedly 

 (Q-analysis), and polar solvents are no con- abnormal in certain diseases. So can the ex- 

 traindications. tent of its deviation from linearity at serum 



Biochemical applications have long been concentrations lower than 10% in isotonic 

 limited to the quantitative determination of saline solution (148-150). Heavy metal hind- 

 total blood serum proteins, following the ing to proteins, because of its specificity for 

 work of Reiss in 1904. The refraction incre- certain functional groups, has long found 

 ment k, per gm % of proteins as determined analytical applications. But the binding of 

 by a suitable Kjeldahl nitrogen analysis smaller ions (Na, K, Rb, F, Mn) also can 

 (132) averages 0.00184, according to Paic be readily demonstrated by interferometry 

 and Deutsch (133). (151-156). Similarly, the binding of organic 



Numerous biochemical investigations, molecules (ascorbic acid (157-158), choles- 



conducted by similar empirical methods, terol (153)) seems to be demonstrable. An- 



have involved the construction of special other large field of biochemical applications 



refractometers and interferometers for the involves the measurement of refraction gra- 



study of streaming fluids, notably by dients by the "schlieren" method, as in elec- 



Cleason (134), Tiselius and Cleason (135), trophoresis experiments. 



Holman and Hagdall (136), Svenson (137), Finally, the complementary character of 



Kegeles (138), Gibert (139), Calvet and reflection, refraction and transmission phe- 



Chevalerias (140), Coulson, Cox, Ogston and nomena of electromagnetic waves make 



Philpot (141), and others. Other empirical these measurements of particular importance 



applications deal with the voluminous body in the newer technology of dielectric films 



of work on the "Abderhalden ferments" and of semiconductors (Conn and Eaton: 



(142). The phenomenon is real, but it still (160)). 



lacks a satisfactory explanation. In general, references 



high precision continuous recording refrac- gee references for the second article of this 



tometry is well adapted to enzymological series (History of Light Refraction), p. 497. 

 studies, to kinetic investigations and to the 



detection of reaction intermediates. Addendum and Bibliography Supple- 



Many other biological problems can bene- ment 



fit from high sensitivity refractometric meas- In recent years the \'olume of published 



urements. The successful titration of highly work on refractometry and interferometry 



diluted antigen-antibody systems was found has reached proportions defying the capa- 



possible, although no detectable precipitate bility of any single investigator. The follow- 



was formed (143-144). Some rather complex ing notes added after setting of the galleys 



systems of this kind have been resolved by represent an almost futile effort to reconcile 



519 



