Organic Acids in the Examination of Minerals. 29 



23. The applications of the methods of examining minerals 

 detailed in the preceding pages are, we believe, numerous and 

 important. Many of the reactions are simple, quickly applied, 

 characteristic, and sensitive ; they may be used, as we have 

 seen, in distinguishing minerals nearly related, and probably 

 in separating minerals mingled in one specimen. The methods 

 will in all probability find useful application in quantitative 

 analysis, a point which we propose to test at some future time. 

 We have already employed a solution of citric acid in the 

 analysis of limestones, for the determination of carbonic 

 anhydride by loss. The evolution of gas proceeds regularly 

 and the limestone is completely decomposed; citric acid pos- 

 sesses an advantage over hydrochloric acid in being non-vola- 

 tile. Experiments to test the accuracy of the method were 

 made with well-dried precipitated carbonate of calcium, and 

 gave results differing by two or three tenths from the theoreti- 

 cal percentage. 



By using the non-volatile organic acids in microscopic work 

 whenever applicable, possible injury to the metallic mountings 

 may be avoided, and in certain cases characteristic phenomena 

 may be observed. 



The importance of the application of these methods to the 

 examination of minerals and rocks in the field is evident. The 

 testimony of various persons as to the practicability of blow- 

 pipe work and chemical work in the field differs greatly, some 

 claiming that it is valuable and easily accomplished, and others 

 that it is altogether impracticable. Professor Geikie, Director 

 of the Geological Survey of Scotland, mentions as a valuable 

 addition to the geologist's outfit, " a small bottle of weak 

 hydrochloric acid, carried in a protecting wooden box or case, 

 of use for testing carbonates ; " and he quotes Sir William 

 Logan as employing acid to test the material adhering to a 

 "limestone spear," with which the underlying strata can be 

 probed.* 



We propose, therefore, the substitution of a stout paste- 

 board box, containing solid citric (or tartaric) acid, for the 



* Science Lectures at South Kensington : Outlines of Field Geology. 1877. 



