Sulfated Residue, Lead, Iron and Copper in Lubricating Oils

In this  methods, the sample  is completely  oxidized  by wet  ashing  with  concentrated  sulfuric acid, concentrated  nitric  acid and  hydrogen  peroxide, or  if  only iron and copper  are  to be  determined, by dry  ashing. To determine sulfated  residue, the  solution obtained by  wet  ashing  is  transferred  to a weighed  dish, evaporated  to  dryness, ignited at 775 degree C, cooled and  weighed. In determining lead, iron and  copper, the  solution resulting  from  the  wet  ashing is  mixed with  alcohol and  filtered  to give  a  precipitate  of  primarily  and  sulfate. This  precipitate  is  boiled  with  sodium carbonate and  then  precipitated  with  hydrogen  sulfide.

Iron  and  copper are  determined on  separate  aliquots  of the  filtrate  from  wet  ashing. The  iron is  separated  as the  hydroxide and  determined colorimetrically  as the  orange  ferrous  orthophenanthroline  complex,  while  copper  is  determined  colorimetrically  as the  yellow diethyldithiocarbamate  complex

Sulfur in Gear Oils

In this method  the sample is vaporized  and  burned in a  stream of air, and  the  oxidation completed  by passing  over  quartz particles  maintained  at a temperature  of 950 to 1000 degree C. The combustion  products are then  passed  through hydrogen  peroxide  which  absorbs  the  sulfur  as sulfuric  acid  and  the  chlorine  as hydrochloric  acid. The  absorbent  is then  analyzed  for total  acidity  and  for chloride ion. The  procedure for  the  determination  of  chlorine  is  included  only  for  correcting   the  sulfur  content  and  the  method is not  recommended  for the  determination  of chlorine  alone.