ANALYSIS IN COMMUNICATION RESEARCH 497 



microtechnique consequently made little progress until a beam balance 

 was produced by W. Kuhlmann of Hamburg, which was capable of 

 weighing to a thousandth of a milligram with no appreciable change 

 in sensitivity with loads up to 20 grams. 



With the perfection of this essential instrument quantitative micro- 

 technique developed rapidly, and because of the economy of time and 

 material it is in many cases actually displacing older methods operating 

 on the usual scale. This is particularly true in organic analysis where 

 the methods are ordinarily tedious and expensive. Pregl, who received 

 the Nobel prize in 1923, worked out rapid, precise micromethods for 

 the determination of carbon, hydrogen, nitrogen and various organic 

 radicles, which require only a few milligrams of sample. As an 

 example of the great practical value of such methods may be cited an 

 instance mentioned by Cornwell ^ in which a complex organic com- 

 pound was synthesized with a yield of about a gram of product. The 

 labor and material involved brought its cost to about $5,000. An 

 analysis was required as a check on the composition, and by the usual 

 methods this would have required 0.2 gram of sample at a cost of 

 $1,000. The analysis was actually made by the micromethod on 2 

 milligrams of sample, cost $10. 



Most of the general equipment originally devised to facilitate micro- 

 operations in qualitative analysis is also applicable to quantitative 

 work. Considerable additional equipment is required, however, for 

 the recovery, conditioning and quantitative measurement of the final 

 transformation products of the analytical process. Precipitates are 

 collected and weighed either by centrifuging in suitably shaped vessels 

 or on suction filters which are essentially miniature reproductions of 

 those used in ordinary work. An innovation in filtration practice 

 consists in the use of an inverted filter which is weighed together with 

 the microbeaker in which the final precipitation takes place. The 

 clear liquid and washings are simply drawn off through the filter. 

 This obviates the necessity of completely transferring the precipitate 

 to the filter, thereby avoiding losses that are otherwise almost certain. 

 Duralumin blocks of various designs have been found excellent for 

 drying and conditioning precipitates. The high heat capacity afforded 

 by the large mass of metal insures a very constant temperature. 

 Various types of micromuffle and combustion furnaces have been 

 devised. Their small size greatly reduces construction costs and 

 permits a more generous use of quartz or platinum linings. 



For the measurement of liquids, microburettes are available which 

 can be read to 0.001 cc. When the quantities are too small for 



• Cornwell, R. T., J. Chem. Education, 5, 1099-1108 (1928). 



