WATEE AXALY.SIS. 289 



SO much potassium permanganate solution that a faint pink 

 tinge remains after four hours. 



Standard Potassium Permanganate Solution. — Dissolve 

 0'395 gramme of pure potassium permanganate in 1 litre of dis- 

 tilled water. 1 c.c. = O'OOOl gramme oxygen. 



Starch Solution. — Make an emulsion of 0'5 gramme of starch 

 in 2 c.c. of water and add this to .50 c.c. of boiling water. Boil 

 for five minutes and cool. 



Phosphates. — Dissolve the ignited residue fi-om the total 

 solid estimation in a little dilute nitric acid ; evaporate the 

 solution to dryness in a porcelain dish, and take up with 1 c.c. 

 of dilute nitric acid, filtej- the solution, and wash the filter paper 

 with very .small amounts of water. Add to the filtrate, which 

 should not exceed 2 or 3 c.c, an equal bulk of ammonium molyb- 

 datc solution and warm to 60" C. (140^^ F.). A yellow coloration 

 is called a " very faint trace " of phosphates, and a distinct 

 precipitate a " very heavy trace." 



Ammonium Molybdate Solution. — Mix 14 c.c. of stioiii; 

 ammonia (sp. gr. "880) with 28 c.c. of water, and add 10 grammes 

 of molybdic acid and stir till all is dissolved. Add this solution, 

 slowly and with constant stirriui;, to 125 c.c. of nitric acid (sp. 

 <.']■. 1 '2) ; stand the solution in a warm place for a fi'w days 

 and decant the clear solution for use. .\ slight deposit nia\- 

 forui on keejMiig. 



Hardness. — To 100 c.c. of the waU^r add 5 drops of metlivl- 



N 

 orange solution, and titiate with hydrochloric acid solution 



till the tint is thi' same as that of 10(1 e.c. of distilled water to 



which five drops of methyl orange and 0'2 c.c. of ;^— acid have 



lieeii added. Subtract <)'2 c.c. from the readinu, and the re- 

 mainder multiplied by i'y will give the alkalinity or temporary 

 hardness in parts per 100,00(1 



Transfer this solution to a porcelain dish, and boil down tt) 

 half its bulk ; pour it in to a lOO c.c. flask, rinsing the basin with 

 well-boiled distilled water, and add a measured volume (10 c.c, 



15 c.c. or 20 c.c). according to the hardness, of a ' solution 



of soda, half carbonate and half hydroxide; make up to near 

 the mark with well-boiled distilled water, cork up, and cool ; 

 when cold make up to the mark, and allow it to stand at least 

 one hour. Filter through a drv filter, and collect an aliquot 



N 



portion (say HO c.c), and titrate with .,t- hydrochloric acid till 



equal in tint to that of the distilled water to which methyl orange 



19 



