WATER ANALYSIS 37 



of barium nitrate be dissolved in I litre of aq. dest. I c.c. = 

 i mgr. Ba(N0 3 ) 2 equal to I c.c. = I mgr. CaC0 3 . 



Total Hardness. Take 50 c.c. of sample in bottle and 

 test with standard soap solution as above until a permanent 

 lather is obtained. Deduct 0-5 c.c. (say) necessary to 

 produce lather, and double the answer gives the total 

 hardness in metrical degrees. This multiplied by 07 

 gives it in grains per gallon, or Clark's degrees. If more 

 than 8 to 9 c.c. be required, it is advisable to dilute 

 25 c.c. of the sample with 25 c.c. recently boiled aq. dest., 

 and redetermine the hardness. 



Permanent or Fixed Hardness. Take 100 c.c. of sample 

 water and make up to 200 c.c. with aq. dest. Boil down 

 to one-half its bulk, and a little more. Allow to cool to 

 6o F. (15-5 C), and make up to 100 c.c. with aq. dest. 

 Remove 50 c.c. and determine hardness as before. 



By boiling, all the free and half-bound CO 2 is driven off, 

 and nearly all the CaC0 3 is precipitated. The CaS0 4 

 and the CaCl 2 are not affected if the evaporation is not 

 carried too far. Some of the MgCO 3 at first thrown down 

 is redissolved as the water cools. 



Temporary or Removable Hardness. This is the difference 

 between the total and the fixed hardnesses. 



Notes. The lime salts precipitate at once with the 

 soap solution ; the magnesium salts* precipitate slowly ; 

 hence it sometimes happens that all the Ca is precipitated 

 and a lather formed which shortly disappears, and more 

 soap solution is needed. The presence of magnesium salts 

 is said to cause the lather to be brown in colour and to 

 break very easily. More soap is required to produce a 

 lather with a certain amount of magnesium, than with 

 the equivalent amount of Ca, though this is ignored in 

 practice. 



2. By Hehner's Alkalimetry Method. 



Temporary. Titrate 50 or 100 c.c. of sample with 

 N/50 H 2 S0 4 , using methyl-orange as indicator, until a 

 permanent pink is got. The sulphuric acid decomposes the 

 CaCO 3 with evolution of CO 2 , and until all the carbonate 

 is decomposed, no sulphuric is free to attack the methyl- 

 orange. The number of c.c. of sulphuric gives the number 



