158 Composition of Waters of Land-Drainaf/c and of Rain. 



In the last instance 10 grains of pui'e sulphate of lime were 

 added with the iodide of silver, but without deran2;ing the result. 

 These results are not selected from a greater number, but were 

 obtained in seven consecutive experiments. The mean of these 

 results is as nearly as possible 0"583 (0*5827), as against 0*585, 

 the quantity of nitric acid experimented upon, or an error of 

 1 in 291 on the whole quantity. The greatest deviation is 

 less than 1 per cent, ; that is to say, that for 100 parts of nitric 

 acid the worst result would show 99. 



If, as is very possible, the nitrate after all was not quite pure, 

 and that the deviations were equal above and below the truth, 

 they are then still further reduced. 



I do not think it necessary to say a word in explanation of the 

 delicacy of a method, which deals with quantities as a whole, 

 which heretofore would have been exceeded by the differences of 

 two expei'lments. 



The following are duplicate analyses of different samples of 

 drainage and rain waters given in the preceding paper — 



Nitric Acid in Drainage Waters (Mr. Paine'). 



* The discrepancy here seen was accounted for by an accident to the pump, 

 -which delayed the experiment. 



