D. D. VAN SLYKE 



samples usually taken for analyses from 100-150 mg. to 4 or 5 mg., 

 and opened a new epoch, not only in organic analysis, but also in 

 organic chemistry. For it became possible to solve problems when 

 amounts of material were available that would have been inadequate 

 even for preliminary analyses by the old macro methods. It is ques- 

 tionable, for example, that the rapid development of knowledge con- 

 cerning the structure of the vitamins would have been possible without 

 these micro methods. The techniques of micro analysis developed in 

 Austria by Pregl and by Emich (1) were brought to this country, es- 

 pecially by J. B. and V. Niederl (3), and are available in a recent 

 volume by these authors. For ultra micro gravimetric work, Lowry 

 (2) has recently described a simple quartz fiber balance which will 

 weigh 200 gammas to 0.03 gamma. 



Volumetric Analysis 



Bang's work (4) introduced micro titrations into biochemistry, 

 utilizing the principle of keeping the volume of titrated liquid small, 

 to maintain the sharpness ^of the end point. Rehberg (9) followed 

 shortly with his micro burette, in which a thread of standard solution in 

 a calibrated capillary of about 1 mm. bore is expelled into the titrated 

 solution by mercury moved by a plunger advanced by turning a steel 

 screw. With this burette, the solution could be measured to within 

 ±0.1 cu. mm., so that 50 cu. mm. was ample for a good titration. 

 Linderstr0m-Lang (7) moved the error down to ±0.01 cu. mm. He 

 used still narrower capillaries, and stirred the titrated solution in a 

 minute glass thimble by a magnetic stirrer consisting of a bit of iron, 

 enclosed in a glass droplet, which was lifted and lowered in the titrated 

 solution by the automatic opening and closing of the circuit to a mag- 

 net. Scholander (10,11) has applied the metal micrometer screw 

 that is readily available because of its general use in accurate industrial 

 mechanical work. The column of standard solution in a fine capillary 

 is moved, as in the Rehberg burette, by pressure of a mercury column 

 advanced by a screw and plunger; but in the Scholander burette the 

 extent to which the screw is turned serves as a measure of the volume 

 of solution delivered, and calibration of the capillary is not necessary. 



A limitation of the Rehberg and Scholander burettes is that they 

 cannot be used to deliver solutions which react with mercury. For 



no 



