PREPARING OPAQUE OBJECTS 393 



hydrochloric acid. For use, dilute one part of this stock solution 

 with twenty parts of distilled water. If upon trial the etching 

 is too energetic, dilute still more; if not energetic enough, add 

 more stock solution. 



Useful in studying bronzes of high tin content and copper 

 alloys in general. 



Ferric Chloride + Alcohol. Robin 1 prepares this reagent as 

 follows : 



Per cent. 



Ferric chloride 5 



Water 5 



Hydrochloric acid 30 



Iso-amyl alcohol 30 



Ethyl alcohol 30 



The etching is rapid and needs careful attention to prevent 

 over treatment, one to three minutes being the average exposure 

 required. 



Valuable in studying aluminum bronzes and brasses. 



Hydrochloric Acid + Absolute Alcohol. To 100 cubic centi- 

 meters of absolute alcohol add i cubic centimeter of concentrated 

 hydrochloric acid. This is the general etching reagent of 

 Martens and Heyn for all iron-carbon alloys. Applicable to all 

 specimens but must be used with care. With extra hard steels 

 and certain alloy steels this reagent does not work well. In 

 these cases Martens suggests the nitric-alcohol reagent. Neither 

 reagent is permanent, but must be freshly prepared for use. 



Hydrochloric + Nitric Acid. Mix three parts of dilute- hy- 

 drochloric acid with one part of dilute nitric acid, add 2 or 3 

 drops of platinum chloride per 100 cubic centimeters of mixture. 

 A valuable etching liquid for copper-nickel alloys. 



Nitric Acid + Absolute Alcohol. To 100 cubic centimeters 

 of absolute alcohol add 4 cubic centimeters of concentrated 

 nitric acid. Prepare just before using. Useful in the case of 

 very hard steels and with certain alloy steels. Especially 

 valuable in developing Troostite. 



Picric Acid -f. Alcohol. Employ a 5 per cent solution of 

 picric acid in absolute alcohol. 



1 Traite de Metallographie. 



