1 2] Precipitation 1 1 



obtained by having both solution and precipitant at the boiling 

 point when mixing them. 



{d) Whenever hot water has no solvent action on the pre- 

 cipitate, it should be thrown down and filtered whilst the 

 solution is hot 



(e) When pouring a liquid from one vessel to another, pour 

 it down a wet glass rod one of whose extremities touches the 

 side of the vessel (see fig. 12). 

 This prevents loss by splashing. 



Exercise V. — Weigh out on a 

 watch glass about -5 gram of am- 

 monia alum. Place this in an 8-oz. 

 beaker, and pour upon it about 50 

 c.c. of boiling distilled water. Stir 

 up the liquid with a clean glass rod 

 until all the solid has dissolved. 

 Now pour dilute ammonia carefully 

 down the side of the vessel until 

 precipitation is complete— i.e., until, FlG> Iti 



after stirring, the liquid smells of 



ammonia. It is easy to make a mistake in testing by the smell of 

 ammonia, as it is quite possible that the air in the beaker may 

 contain a little ammonia gas even before the liquid has become 

 ammoniacal. It is therefore necessary to blow the ammonia 

 fumes away before smelling ; or a piece of red litmus paper may 

 be added. When this has become blue the liquid contains excess 

 of ammonia. Place the beaker over a Bunsen burner and heat 

 just to boiling, keeping it covered the while with a clock glass. 

 Place the beaker on one side to settle. 



FILTRATION AND WASHING 



12. These operations are exactly like the ones with which 

 the student is familiar. More care, however, is required for 

 quantitative than for qualitative analysis. The following in- 

 structions will show the principal precautions required : 



(a) Special quantitative filter paper should be used* This 



