QUANTITATIVE ANALYSIS 



The eye strain and subjective error accompanying the use of a 

 visual instrument are obviated in most of the modern photometers by 

 using photocells to measure the intensity of the transmitted light. The 

 rapidity with which a series of observations can be carried out is also 

 much greater when the eye is replaced by the photocell. 



A further advantage of the photometer is that, with photocell 

 measuring devices, it can be used with light waves extending into the 

 ranges of the ultraviolet and infrared, broadening the range of ac- 

 cessible analyses. 



In the ultra micro colorimetric methods which Richards and 

 his collaborators (24) developed for analyses of samples of 1 cu. mm. 

 of glomerular filtrate, the sample is drawn into a small glass capillary 

 in which it is mixed with chromogenic reagent, and the color is esti- 

 mated by comparing the capillary under a microscope with a series of 

 standards similarly prepared. The comparison with graded standards 

 is a return to simplest first principles, but the technique of the applica- 

 tion gave results to 1%. 



Fluorimetric Analysis 



The diffuse fluorescent light developed by passing light rays 

 into solutions of fluorescent substances (28) can be measured by the 

 same visual or electrical means employed in colorimeters and photom- 

 eters, and serves in some cases, such as determination of riboflavin 

 (27), quinine, atabrine (26), and related compounds, to measure 

 substances in more dilute solutions than can be handled with a photom- 

 eter. In fluorimetry, the concentration of fluorescent substance is 

 directly proportional to the intensity of the light measured, instead of 

 being inversely proportional to the log of the transmission, as in pho- 

 tometry. 



Po larograph ic A nalys is 



This procedure, which has gained rapid utility during the past 

 few years, was introduced by Heyrovsky in Prague in 1925, and has 

 been applied to a multiplicity of analyses of substances, both organic 

 and inorganic. It is based on measurement of the amperages obtained 

 at observed voltages applied to solutions of electroreduciblc or electro- 



