756 



DR CHARLES HUNTER STEWART ON THE ESTIMATION OF 



Experiment V.: — 



Edinburgh Main Water, 

 >) 

 )> 

 To these were added 



+ 2 - 96 grains nitrate of potassium per gallon, 

 t3"93 „ ,, „ 



0-2418 

 0-2418 



, .£1+"!! 



I -|-2'9o 



0-0180 



000 



000 



0-0180 

 0-01878 



rous sulphate, 



Iii the foregoing experiments the mark ( ) means carbon not determined. 



From the above experiments, it is evident that, when the amount of nitrate in a water 

 exceeds 1 grain per gallon of nitrate of potassium, it begins to have an effect on the 

 nitrogen ; and at less than 3 grains per gallon the nitrogen in such waters as were 

 examined entirely disappears. In many highly polluted waters, when analysed by 

 Kjeldahl's method without previous decomposition of the nitrates, there was no organic 

 nitrogen at all found. The treatment by ferrous sulphate always gave consistent results. 

 Though surface waters, like those analysed by Messrs Drown and Martin, contain, 

 as a rule, very little if any nitrate, a very large number of waters do. The author has 

 repeatedly this year examined waters with as much as 20 grains nitric acid (N 2 5 ) 

 per gallon. These were waters in use for drinking purposes. If the report of the 

 Commission on the water supply of Britain (1876) be consulted, it will be seen how 

 many drinking waters have more than 1 grain per gallon. 



Note. — Since the results on Table I. were obtained, the author has modified the apparatus slightly. The 

 bulb on the inlet tube with its rubber and clip arrangement has been replaced by one having two well-ground 

 stoppers, the one at the point of junction of the bulb with the tube and the other in the upper and outer 

 opening. This permits of the sulphuric acid being added without opening the flask as well as of adding the 

 permanganate solution. (See Fig. 5.) 



Table I. 



Name of Substance. 



Weight taken. 



Calculated 

 from Com- 

 bustion. 



Found. 



Difference. 



Percentage by 

 Combustion. 



Percentage by 

 New Method. 





Milligrams. 



Milligrams. 



Milligrams. 



Milligrams. 







Urea, . 



75 



15-84 



15-79 



•05 



21-12 



21-05 



>> 







51 



10-77 



10-89 



•12 



n 



21-37 



j> 







28 



5-91 



5-88 



•03 



>> 



21-00 



j) 







10-44 



2-20 



2-23 



•03 



) ? 



21-42 



Uric Acid, 







38 



13-88 



13-88 



o-o 



36-53 



36-53 



„ 







10-6 



3-87 



3-89 



0-02 



)» 



36-69 



!> 







8-2 



2-99 



2-90 



0-09 



?> 



35-50 



» 







7-0 



2-55 



2-51 



0-04 



>> 



35-86 



Creatine, 







50-84 



19-02 



18-46 



0-56 



37-43 



36-29 



>> 







20 



7-56 



7-47 



0-09 



>) 



36-99 



>> 







16-12 



603 



5-82 



0-21 



)> 



36-19 



>> 







9-78 



3-58 



3-54 



0-04 



?» 



36-95 



Narcotine, 







22-33 



14-29 



14-03 



0-26 



63-92 



62-84 



M 







13-62 



8-71 



8-63 



0-08 



J) 



63-38 



>) 







4-61 



2-94 



2-89 



0-05 



)» 



62-66 



Naphthaline, 





956 



8-96 



9-00 



0-04 



93-75 



94-14 



)> 





4-42 



4-14 



4-14 



o-o 



i) 



93-75 



