276 § 141. BEVERAGES. 



all but 1-2 c.c. of the solution of soap that will be 

 required, and then allow it to flow in drop by drop only, 

 until the reaction is ended. 



The relation between the quantity of the standard solu- 

 tion used and the hardness of the water is given in Table 

 YIII. If the water tested was diluted with distilled water, 

 the hardness is to be taken as many times greater as the 

 volume of the water was increased by the dilution. 



If a water contains more than 12 parts of lime in 

 100,000, the first addition of the solution of soap to it 

 causes the formation of a flocculent precipitate, and it 

 must be diluted as above before the test is made ; if less 

 than this proportion of lime is present, only an opalescence 

 appears in the liquid on adding a drop of the solution of 

 soap. 



With respect to the hardness of water, we have to dis- 

 tinguish the total hardness, which is caused by the total 

 amount of lime in the water, and the permanent hardness, 

 caused by salts of lime that are not precipitated when the 

 liquid is boiled, such as calcic sulphate and chloride. To 

 determine this permanent hardness,^boil 300 to 500 c.c. of 

 the water half an hour, in a flask of twice the capacity, 

 replacing the water, as it is evaporated, by fresh distilled 

 water ; after the liquid has cooled, make its volume the 

 same as that with whicli the operation was begun, by 

 adding more water, mix the wliole well together, filter 

 the liquid, and determine the permanent hardness in an 

 aliquot part of it, as above. 



2. FlecTc's method. — This apparently convenient method 

 depends upon the fact that, Avhen a solution of soda-soap 

 in alcohol is added to a solution of a calcic salt, a neutral 

 sodic salt is formed, and that, as soon as all the calcic salt 

 is decomposed, the addition of more soda-soap will turn 

 red litmus blue. {Fresenius^s Zeitschr/ft, 7, 351.) 

 . T/ie Standard Solutions. — Solution of Soap. — Cut 50 



