266 Domestic Science 



bath to boiling. The heat evolved during the con- 

 densation of a portion of the steam on the bottom of 

 the dish will cause the water in the dish to evaporate 

 slowly. When it has all disappeared run in another 

 25 c.c. and again evaporate to dryness. Similarly treat 

 two further quantities of 25 c.c. Allow the dish to 

 cool and. weigh it once more. The increase in weight 

 will be that of the solid matter dissolved in 100 c.c. for 

 all practical purposes the weight of this may be taken 

 as 100 g. of the tap-water. 



Should other supplies of water be readily available, 

 the percentage of dissolved solids may be found in 

 similar fashion. River-water, spring-water and rain- 

 water can usually be tested without much difficulty 

 with regard to obtaining supplies of any one of them. 



184. In cases where the quantity of dissolved solid 

 matter in a water-supply is not excessive, and no 

 deleterious substances are to be found among those 

 dissolved, the removal of the solids in solution is not 

 necessary. Where, however, the presence of a specially 

 large amount, or of harmful bodies, is known, recourse 

 is had to the process of distillation in order to get rid 

 of the solids. In this process, advantage is taken of 

 the observation already made that the solids are not 

 easily vaporisable and remain in the vessel in which 

 water is boiled. 



EXPERIMENT 121. Half fill the body of a tubulated 

 (i.e. stoppered) retort with tap-water. Arrange the 

 retort upon a stand with its neck dipping into a small 

 flask, which floats on the surface of water in a large 

 earthenware trough, as indicated in Fig. 85. Heat the 

 water in the retort to boiling-point by means of a 

 small Bunsen flame. Some of the steam produced will 

 condense in the neck of the retort and in the flask. 



