THE EXAMINATION OF WATER 655 



(3) Detection and Estimation of Poisonous Metals. 



To 100 c.c. of the water add a few drops of acetic acid. 

 Pass in H2S. 



A light clear brown deposit = copper. 

 A dirty granular deposit = lead. 

 Copper. 



To another 100 c.c. add a little acetic acid. 

 To this add 2 c.c. of fresh solution of potassium ferrocyanide. 

 To estimate the amount of copper present : — 

 Match this chestnut brown colour by a standard copper solution. 

 Copper solution (i c.c. = o'cooi grm. Cu) as is described in 

 Nesslerizing the ammonia solutions. 

 Lead. 



To 100 c.c. of water add a little acetic acid. 

 To this add a few drops of potassium chromate and stir well. 

 A yellow turbiditv (of lead chromate) indicates lead. 

 If lead is in excess a yellow deposit will be formed. 

 Pass H.S in 100 c.c. of the sample. 



Match the brown coloration wilh a standard lead solution 

 (i c.c.=o"oooi grm. Pb) to estimate lead. 

 Example, 12 c.c. of the standard solution are necessary to match 

 the colour in the given sample. 



Hence there is o'oooi x 12 grm. of lead in the 100 c.c. of the sample, 

 there is qooqi x 12 x ico.o r-2 grm. Pb in 100,000 parts. 



ICO 



Iron. 



If neither copper nor lead is present test for 'won. 



Take 100 c.c. of the sample. 



Add 5 c.c. of nitric acid, i in 5. 



Then 5 c.c. of 10 per cent, potassium sulphocyanide. 

 A red coloration indicates iron. 



Match this colour with a standard iron solution (i c.c. = o'cooi 

 c.c. grm. Fe) to estimate the amount. 



If the colour is too intense to be matched conveniently take a 

 smaller amount and dilute to 100 c.c. with distilled water. 



(4) To Detect and Estimate Chlorine, 



This is present in most waters as sodium, potassium or calcium 

 chloride. 



Its presence may be due tO' : — 



(i) The water passing through saline compounds in the strata, 

 e.g., sandstone, greensand. 



(2) Pollution bv organic matter, especially urine. 



(3) Deep wells near the sea coast. 



(4) Tidal rivers. 



