208 Water Analysis [348, 349 



solution into the bottle. Replace the stopper, and shake 

 vigorously. A lather will be formed, which may or may not 

 disappear on standing. Should it disappear, add another c.c, 

 and repeat the operation until a permanent lather is formed. 

 Note the quantity of soap solution required, and repeat the 

 operation, running in o*i c.c. at a time when the correct 

 quantity is nearly reached. When the amount has been 

 correctly determined, calculate the dilution necessary to bring 

 the solution to such a strength that ioc.c. of the CaCl 2 solution 

 diluted to 70 c.c. with water requires just 1 1 c.c. of soap solu- 

 tion. A calculation of this kind has been described in 

 paragraph 62. Dilute to the extent which the calculation shall 

 direct with alcohol (35 per cent.), and with the new solution so 

 formed repeat the experiment. The solution will not give quite 

 the result expected, and will probably have to be diluted again 

 after making a fresh calculation. Repeat this alternate titration 

 and dilution until n c.c. of soap just gives a lather with 

 10 c.c. of calcic chloride and 60 c.c. of water. 



348. Total Hardness. — To determine the total hard- 

 ness, measure 70 c.c. of the water under examination into the 

 stoppered bottle and run in soap solution, as described in 

 the last paragraph, until a permanent lather is formed which 

 will not subside in three minutes. Read off the number of c.c. 

 of soap required. It requires 1 c.c. of the soap to produce a 

 permanent lather with 70 c.c. of water ; therefore we subtract 

 1 c.c. from our reading, and enter our result as degrees of 

 hardness. Thus, supposing that 9*5 c.c. had been used, then 

 we should say the total hardness of the water was 8*5 degrees, 

 or that 1 gallon of it contained salts of calcium and mag- 

 nesium equivalent in soap-destroying power to 8*5 grains of 

 calcic carbonate. 



349. Permanent Hardness. — Measure out 250 c.c. of 

 the water, and boil gently for half-an-hour. Cool, dilute with 



