CHEMICAL ANALYSIS. 41 



The number of inquiries received as to tin- method- u>cd in !he chem- 

 ical analysis ,,f rocks, clays, cements, etc.. has shown that in spite of 

 the great number of texi hooks on technical chemical anal\ ->is. there 

 is a demand for methods of rock and clay analysis which shall In- at 

 the same time practical, rapid, and accurate enough f or ((,,. pui-po-c 

 in hand. 



The methods as given in detail in the Appendix have been tested in 

 the hands of several workers on a large number of samples, ami have 

 been found to yield satisfactory results when compared with more 

 complete and accurate work. Analysis is always made on air-drv 

 samples, as the directions usual!} 7 given in text-books for operating 

 on samples dried at 100 C. invariably lead to bad results, since pla>t it- 

 clays and rock powders reabsorb comparatively large quantities of 

 water from the air after being heated/' 



By following the scheme of anatysis given in the Appendix several 

 analyses can be completed by one man in one working day, provided 

 the fusions have been made on the preceding day and the evaporation 

 for the separation of the silica allowed to go on over night. There is 

 no claim made that these short cuts yield results as accurate as more 

 precise and tedious methods; in fact, any scheme of analysis which 

 divides a gram sample into live aliquot parts is open to criticism, as 

 each determination, with the exception of the silica, has its error 

 multiplied by five. Nevertheless, if the pipette for dividing the solu- 

 tion is accurately standardized to deliver exactly the fifth of the con- 

 tents of the half-liter flask used, the summation of the complete 

 analysis comes within 0.5 per cent of 100 in the large majority of 

 analyses. 



Among the rarer or more unusual elements only manganese and 

 titanium are included in the scheme of analysis. Undoubtedly other 

 elements, such as chromium, barium, strontium, zirconium, lithium, 

 chlorin, and nuorin are present in many rocks and clays, but usually 

 the amounts are so small that for practical purposes they can be 

 ignored. Titanium, on the other hand, is rarely absent and is not 

 infrequently present to the extent of several per cent. Although the 

 effect, if any, of titanium on the properties of clays and cement- i- 

 not known, it is certainly wrong to report this constituent as alumina, 

 as is nearly always done. 



THE APPLICATION OF LABORATORY RESULTS TO PRACTICE. 



The proper interpretation and application of the results obtained in 

 the laboratory are quite as important as the general accuracy and 

 appropriateness of the tests themselves. It i< probable that many 

 engineers and others interested in the subject of road building who 



Cushman. Jour. Am. Chem. Soc., May, 1903. 



