ANALYSIS IN COMMUNICATION RESEARCH 495 



deposits on the wire from which it is sul)st'(iiu'ntl\- (Hstillcd. As Httle 

 as 0.001 mgm. can he readily detected in this \va>'. 



A considerable part of the microanalyst's task is the physical isola- 

 tion and recovery of the material on which his analytical operations 

 are to be performed. His problems very often recjuire examinations 

 of minute particles or aggreiiates of foreign substances which have 

 become attached to or embedded in the surface of a material. He 

 may also be required to isolate and study the structural units which 

 compose a given formation. For e.xample, a deposit occurs on the 

 surface of a metal as a result of corrosion. This deposit is not of a 

 homogeneous nature but is built up in successive layers, each of which 

 differs in composition. To obtain a satisfactory picture of the mech- 

 anism of the production of the deposit it is necessary to know the 

 composition of each separate layer. 



The mechanical manipulations necessary to obtain sample material 

 frequently tax the analyst's ingenuity more than the analysis itself. 

 The work is usually carried out under the low powers of a microscope, 

 preferably of the binocular type. Much of the technique of the 

 biologist has been appropriated by the microanalyst in this phase of 

 his work. Various types of dissecting tools find ready application 

 here. The dental engine with its various attachments, such as drills, 

 burrs, carborundum w heels, has been found extremely useful for drilling 

 out inclusions in metals and for the removal of hard surface films. 

 The micromanipulator, an instrument originally designed by biologists 

 to perform intracellular operations, has recently been employed in 

 microchemical work with very satisfactory results. This instrument 

 furnishes the means of regulating with great precision the movement of 

 needles, capillary pipettes, electrodes, electrically heated platinum 

 wires, etc., under relatively high magnifications. It offers great 

 promise where particles of exceptionally small dimensions are to be 

 studied. 



A number of methods have been developed and used by the Labora- 

 tories' Microchemical Group for the collection and study of central 

 ofiice dusts. A device which deserves particular mention is the 

 impinger, an adaptation of which has been employed to remove dusts 

 from the extremely localized area represented by a single relay contact 

 point. The device is so constructed that the particles, after being 

 picked up by suction, are projected at high velocity against a micro- 

 scope slide, the surface of which is coated with an adhesive medium. 

 The slide is removed from the apparatus and the dust subjected to 

 physical and chemical treatment to determine its nature. 



In quantitative microanalysis, the analyst is faced with the added 



