MABERY. — DETERMINATION OF SULPHUR. 5 



placed in the forward portion of tlie combustion tiibe in the zone of 

 greatest heat ; if it terminates at the narrowest point of tlie constric- 

 tion, eontmuous combustion is insured by thorough admixture of the 

 volatilized substance with oxygen. Complete oxidation is still more 

 certain in rapid combustion if that portion of the tube in front of the 

 narrower part is left somewhat longer than is preferred by Sauer, 

 Mixter, or Burton. The tubing we have in use is somewhat thicker 

 in the wall than that in ordinary use, and larger, with an inside diame- 

 ter of 18 mm. It is important that the oxidation proceed as rapidly 

 as is consistent with complete absorption, and we find that this is best 

 accomplished in a large U tube partly filled with broken glass. Our 

 U tube is 34 cm. in height, 25 mm. inside diameter, and with 50 c, c. of 

 the absorbent solution a rapid gaseous stream may be passed through 

 without danger of loss. For low sulphur oils we use a solution of 

 sodic hydrate of such a strength that 1 c. c. equals 0.0010 gram of 



ill 



r 



Fig. 3. 



sulphur, and for higher percentages a solution in which 1 c. c. equals 

 0.0050 gram. Methyl orange has been used as an indicator in all 

 our determinations ; the change in color in titrating an alkaline solu- 

 tion with this indicator is well defined and exceedingly delicate. The 

 titrations may be made in the U tube without transferring the solution 

 after washing in the acid from the combustion tube. To carry for- 

 ward the volatilized substance it is advantageous to introduce a slow 

 current of carbonic dioxide, as proposed by Mixter, and we have some- 

 times used a combustion tube closed with a rubber cork in front and 

 sometimes a bent tube. With substances containing a high percentage 

 of sulphur it is doubtless safer, as Mixter suggests, to avoid the use of 

 a cork in front. 



