Subsurface Laboratory Methods 233 



pattern matching in spacing and intensity all the lines of the original 

 pattern, when both patterns are prepared under identical conditions of 

 exposure and processing. If line shifts, fading of the pattern in general 

 with increasing values of the 29 angle, or other differences are observed 

 in the patterns, irregularities of composition, such as solid solutions, are 

 indicated and the compound composition of the specimen must be deter- 

 mined by calculation from a chemical analysis. The chemical analysis 

 frequently is best accomplished by means of standard spectrographic pro- 

 cedures. For thorough study of mixtures of silicates, the methods of 

 X-ray-diffraction analysis *^ ^^ ** are practically indispensable. These meth- 

 ods reveal the various chemical combinations in which the silicon exists, 

 whereas chemical or spectrographic methods alone yield only the total 

 amount of silicon in the unknown, giving no clue as to its mode of com- 

 bination. 



Recently the American Society for Testing Materials has announced 

 the completion and availability in the near future of the new second 

 supplementary set of index cards. The original and first supplementary 

 sets will now be available in the revised form only. Each set includes data 

 for approximately 1,400 compounds. 



In the original and first supplementary sets, the values of the d-spac- 

 ings corresponding to the three strongest lines, together with their 

 corresponding relative intensities, appear in the upper left-hand corner of 

 each card (See pi. 6). There are three cards in the file for each diffrac- 

 tion pattern; the first card has the strongest line of the pattern at the 

 extreme left and also contains the complete pattern data and some crystal- 

 lographic data where available. The second card has the second strongest 

 line in this position, and the third has the third strongest line in this 

 position. The cards with the second and third strongest lines at the extreme 

 left position were only "follow" cards and did not contain any data other 

 than the d-spacings corresponding to the three strongest lines. The cards 

 are filed in straight numerical order. 



The revised original and first supplementary sets and the second 

 supplementary set include only one card for each pattern, so as to reduce 

 the required number of cards. These cards also include the data for the 

 d-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, additional data 

 consisting of the data for the X-ray set-up, crystallographic information, 

 optical information, and information concerning the source, preparation, 

 heat treatment, etc., of the sample are given. In addition, the card con- 



^ Clark, G. L., and Reynolds, D. H., Quantitative Analysis of Mine Dusts: Ind. and Eng. Chemistry 

 Anal. Ed., vol. 8, pp. 35 ff., 1936. 



*^ Ballard, J. W., Oshry, H. I., and Schrenk, H. H., Quantitative Analysis by X-ray Diffraction I. 

 Determination of Quartz: Bur. Mines Rept. Inv. 3520. 



■•^ Ballard, J. W., and Schrenk, H» H., Routine Quantitative Analysis by X-ray Diffraction: U. S. 

 Bur. Mines Rept. 3888. 



