Alphabetical and Grouped Numerical Index of X-ray Diffraction Data (Special 

 Technical Publication No. 48-E, A.S.T.M.) is now furnished with these data 

 cards. This book lists each pattern in three different places; i.e., as if each of 

 the three strongest lines were actually the most intense line in the pattern. 

 Pattern searching by means of this book greatly reduces the labor involved. 

 These cards also include the data for the c?-spacings corresponding to the three 

 strongest lines of the pattern listed in decreasing order of intensity in the upper 

 left corner of the card. The data for the largest spacing of the pattern are given 

 to the right of the data for the three strongest lines. Wherever available, addition- 

 al data consisting of the data for the X-ray setup, crystallographic information, 

 optical information, and information concerning the source, preparation, heat 

 treatment, etc., of the sample are given. In addition, the card contains the 

 formulas (chemical and structural for organic compounds), name, and complete 

 pattern data. The cards are arranged into small Hanawalt groups of convenient 

 size for values of the strongest line, and each group is arranged in numerical 

 sequence according to the values of the second strongest line. This difference 

 between the old and the revised-card indices will, of course, alter the above- 

 described procedure somewhat when the revised index is used. With the revised 

 index, the search of the diffraction-data file starts with two lines chosen from 

 the unknown pattern as the strongest and second strongest. If this choice does 

 not locate a corresponding X-ray pattern, it is necessary to reverse the order of 

 the lines and search again. 



It may even be necessary to try various other combinations of strong lines 

 in the pattern before the identification can be made. For those who wish to 

 continue the original method of searching the data file, the Society offers addi- 

 tional sets of the revised cards at reduced prices. 



When considerable investigation is being carried out in a limited field, or 

 if sufficient optical or other data are available so that the possible compounds in 

 unidentified specimens are relatively small, it frequently is advantageous to 

 build up a file of patterns of standard materials. These patterns can then be 

 used for identifying unknowns by direct comparison with their patterns. Figure 

 9-10 illustrates this method. However, it is to be strongly emphasized that 

 extreme caution must be observed in selecting the materials for these standard 

 patterns. Errors in identification are found frequently even for specimens 

 obtained from established museum and private mineral collections. 



Direct comparison of patterns, when used together with the Hanawalt 

 method described above, but using the standard patterns in place of the cards 

 is the most satisfactory for identification of materials, both in accuracy and time 

 saved in the anlysis. Occasionally, the Hanawalt method fails for mixtures be- 

 cause several strong lines of different ingredients fall in juxtaposition on the 

 pattern and consequently are considered as a single broad line in the interpre- 



168 



