66 LIFE: ITS NATURE AND ORIGIN 



to undergo severe cold work this element should be excluded. Anti- 

 mony exerts a similar influence in copper and its alloys, and brass is 

 practically unworkable if it contains 0.005 per cent of this element." 

 As little as 0.001 per cent of boron in steel necessitates a change in its 

 heat treatment. The crystallization of primary silicon in alumi- 

 num/silicon alloys (12 per cent Si) is inhibited by 0.002 to 0.01 per 

 cent of metallic sodium. Such facts indicate the great importance of 

 segregating the different kinds of metal scrap. 



The polarograph, electron diffraction, infrared spectrography, the 

 mass spectrometer, and chromatography are all useful in analysis. The 

 last depends upon the differential diffusion of substances down a 

 column of a selected adsorbent, under the influence of a stream of a 

 selected "solvent." 



With many biological substances, micro-analysis is resorted to, the 

 total amount of a sample often being less than a milligram, and the 

 substance sought being present only in gammas (1 gamma is 1/1,000,000 

 milligram). But still more minute traces can be determined by tests 

 with living organisms, e.g., by immunological reactions, or by the 

 effects shown on the growth of yeasts or plant seedlings. Yeast tests 

 show that biotin has a detectable effect in a dilution of one part in 

 400 billion. Dr. Joseph Needham of Cambridge describes 3 an ingeni- 

 ous application of the Cartesian diver 4 ultramicromanometer (origi- 

 nally designed by K. Linderstr0m-Lang) to measure the minute range 

 of gas exchange in the developing gastrula. Needham estimates the 

 approximate sensitivity of the unit as 0.00015 to 0.001 microliter 

 of gas. 



The chemical properties of the recently synthesized element pluto- 

 nium were determined at first on an ultramicrochemical scale. Pro- 

 fessor Henry D. Smyth states 5 that "one microgram (1/1,000 mg) is 

 considered sufficient to carry out weighing experiments, titrations, 

 solubility studies, etc. . . . Successful microchemical preparation of 

 some plutonium salts and a study of their properties led to the general 

 conclusion that it was possible to separate plutonium from the other 

 materials in the pile." 



The Effects of Trace Substances 



In some cases, small amounts of certain substances exert a bene- 

 ficial effect; the following will serve by way of illustration: 



Helpful Traces 



Gasoline: 0.06 per cent of tetraethyl lead inhibits "knock." 

 Rubber: Nitrogenous substances in crude Para facilitate the 

 "cure." Purer plantation rubber demands accelerators. 



