278 TITRIMETRIC METHODS 



the water by heating on a hot plate before proceeding to the ashing. 



2. Dissolve the ash in 5% sulfuric acid, and, if the insoluble form 

 of ferric oxide is present, remove the acid extract and heat the moist 

 residue on a hot plate until sulfur trioxide fumes appear. Then dis- 

 solve the residue in 5% sulfuric acid and add the liquid to the first 

 extract. 



3. Pipette soln. of sample into a microreductor (Fig. 48, page 

 171) and adjust acidity so that when diluted to vol. the acid con- 

 centration will be 0.1 A^. Usually 40-75 /xl. 5% sulfuric acid is re- 

 quired for solns. of ashed samples. 



4. After the vol. is made up to the mark, add 30 ul. 3% cadmium 

 amalgam; stopper and shake at intervals or continuously for 10 min. 



5. Pipette about twice the vol. of 0.01 N eerie sulfate needed to 

 react with the unknown into a dish (Fig. 44, page 169). Add a meas- 

 ured quantity of indicator soln. and start the thread stirrer. 



6. Open the reductor and pipette an aliquot into the eerie sulfate 

 soln. 



7. Titrate with ferrous ammonium sulfate to a permanent reddish 

 tint. 



8. Run a control by titrating the eerie sulfate without a sample. 



Ramsay Method for Iron 



SPECIAL REAGENTS 



Concentrated Sulfuric, Perchloric (60%), and Nitric Acids. Test 

 the nitric acid for iron and distill from glass, if necessary. 



50% Potassium Thiocyanate. 



0.02 to 0.05 N Titanous Sulfate (depending on the quantity of iron 

 and the bore of the burette). Pour 200 ml. freshly boiled distilled 

 water into bottle F (Fig. 93) with stopcocks C, D, and G closed. 

 Mix the proper amount of com. 15% titanous sulfate or chloride 

 with 10 ml. water and 10 ml. cone, sulfuric acid. Boil the mixture 

 vigorously for 1 rain. Pour at once into F; stopper immediately. 

 Open stopcock D and let stand overnight for any precipitate 

 to settle. Then close D, open C, and allow a brisk stream of hy- 

 drogen to bubble through .4. Close C, and open first D and then G 

 to force the standard soln. over the siphon into the burette. A soft 

 vacuum grease (W. Edwards and Co.) was used for the stopcocks, 

 but perhaps silicone grease would be better. Standardize daily 

 against a standard ferric ammonium sulfate soln. 



