METALLOGRAPHY 



(d — s) to (d + s) includes about 68 % of the 

 particles. 



Other functions which fit distributions 

 often encountered are (1) the log normal 

 distribution : 



/(d) = 



log Sg-\/2ir 



exp 



■ _ / \ogd - log dg \ 



^ \ log Sg ) 



(2) the Rosin-Rammler function: 



dio 



where Sg is the standard deviation of the 

 logarithms of the diameters, dw/d(d) is the 

 weight falling within a narrow size range 

 d{d), and a, h, and c are constants. 



Cumulative curves are often used to rep- 

 resent particle size distributions graphically. 

 These are curves which result from plotting 

 the percentages of particles greater than (or 

 less than) a given particle size against the 

 particle size. The ordinate can represent the 

 percentage of total surface or of total weight 

 instead of the percentage of the number of 

 particles. When the diameters are normally 

 or log normally distributed the cumulative 



curves are straight lines when plotted on 

 ''probability" or "log probability" graph 

 paper, respectively. Such paper is commer- 

 cially available. 



A very large number of methods have 

 been proposed for determing the sizes of 

 particles, but most of them are based on one 

 or more of a small number of principles. 

 Optical microscopy is often used for particle 

 size determination. It has the advantage that 

 the particles are observed directly and that 

 the basic equipment is relatively inexpensive. 

 However, it is a very tedious method if ac- 

 curate results are to be obtained and is sub- 

 ject to large sampling errors unless adequate 

 precautions are taken. 



Richard D. Cadle 



PLASTICS. See GENERAL MICROSCOPY, p. 

 390. 



PROJECTION MICROSCOPES See ENGINEER- 

 ING MICROSCOPES, p. 438. 



PULP AND PAPER. See GENERAL MICROS- 

 COPY, p. 394. 



SCHMALTZ PROFILE MICROSCOPE. See EN- 

 GINEERING MICROSCOPES, p. 438. 



STEREOSCOPIC MICROSCOPE. See ENGI- 

 NEERING MICROSCOPES, p. 439. 



Metallography 



INDUSTRIAL RESEARCH, APPLICATIONS TO. 



See GENERAL MICROSCOPY, p. 363. 

 TRANSMISSION ELECTRON MICROSCOPY OF 



METALS— DISLOCATIONS 

 TION. See p. 291. 

 WEAR AND LUBRICATION. 

 MICROSCOPY, p. 308. 



AND PRECIPITA- 



See ELECTRON 



MiCROMETRON AUTOMATIC MICROSCOPE 



The micrometron is a new microscope images. It is often necessary to scan sys- 



which provides a fully automatic stage tra- tematically over large areas of tissue section 



verse mechanism combined with accurate in order to reveal a simple central truth rela- 



photoelectric observation of the microscopic tive to normal or pathological state, or to 



468 



