CHEMICAL ANALYSIS 47 



permanganate, if used at an early stage, caused a loss of 

 nitrogen, added at the end it completed the reaction and gave 

 a higher ammonia.^ The residue is cooled, diluted, neutralized 

 with saturated sodium carbonate, distilled and Nesslerized. 

 Chlorides in large quantities, nitrates and nitrites up to 

 1*5 parts per 100,000 together, did not cause loss of organic 

 nitrogen in the process. 



Dr. McGowan- undertakes a determination of the total 

 nitrogen in all forms. He adds sugar solution, then slowly 

 reduces the nitrate and nitrite to ammonia by Zn and dilute 

 H2SO4, Kjeldahls with H2SO4 and sodium sulphate, and distils 

 with potash into standard acid as above. But he describes the 

 process as taking about six days with continual attention, and 

 says at the end that it answers " in sewages, tank or precipita- 

 tion liquors, and (with care) in effluents of average quality. 

 With very pure effluents . . . the errors of experiment are too 

 great for this indirect method for the determination of * X ' 

 nitrogen and total organic nitrogen to be of value at present." 

 The process is not, therefore, better than the simple one we 

 have first given. 



Dissolved Oxygen. — I have described and reviewed a number 

 of processes for the determination of the oxygen in sewage 

 and waters in the Analyst of June, 190 1 ; most of them, like 

 Schutzenberger's and Thresh's, are not convenient for general 

 use away from the laboratory.^ As it is very important to be able 

 to ascertain quickly on the spot the absorption or disappearance 

 of free oxygen in a sewage or effluent, I have adopted the simple 

 process introduced by Winkler, which gives sufficiently near 

 results. An accurately stoppered bottle, of which the contents 

 are known when full, is completely filled with the sample. 

 A convenient volume is 250 to 300 c.c. One c.c. of a 

 nearly saturated solution of manganous chloride is passed to 

 the bottom by a long pipette, then 3 c.c. of 33 per cent, caustic 

 soda containing 10 per cent, of KI are similarly added. The 

 stopper is inserted, and the bottle moved round so as to mix 

 the whole. The MnO absorbs the free O and becomes brown. 

 The whole is allowed to settle, then 3 c.c. of concentrated HCl 

 are passed to the bottom without any bubbling of air, when 

 iodine is liberated in proportion to the free O. The contents, 



1 Permanganate is liable to contain ammonia, and give turbid Nesslers. 



■•^ Report to Royal Sewage Commission, vol. iv., part v., 1904, p. 26. 



'■' Joiirn. Soc. Chem. Ind., xv,, 15, xviii., 340; Chemical News, May 30, 1902. 



