the Substances usually present in Water. 37 



the ware now generally sold under that name. A glass flask is pre- 

 ferable, and much more convenient, the water in it being made to boil 

 briskly on a sand-bath, or over a lamp or chauffer of charcoal. A 

 Florence oil flask is better than a flint glass one, being of a harder 

 glass, less easily attacked by the boiling water, and though it can be 

 filled little more than half full at the outset, as the water is boiled 

 off, it may be filled up by pouring in the remainder of the water 

 through a funnel so as not to touch the empty part of the flask, 

 and doing this smartly before the issuing steam has time to heat the 

 neck of the funnel. In this case there is no risk of breakage. 



Should it be required to evaporate to complete dryness, this is 

 best done by using the flask until about 300 grs. of liquid only 

 (unless the water be very saline) remain. This is poured out into a 

 platina vessel, a capsule of German porcelain, or the lower part of a 

 flask cut off, washing out any sediment from the flask by distilled 

 water, and adding it to this fluid remainder. From such a vessel it 

 can be easily removed after all the moisture is dissipated. 



In precipitating the different substances, wine glasses do not 

 answer, as the matter thrown down adheres to their conical sides. 

 Test tubes for small portions, and tall vials with flat bottoms for 

 larger, answer much better. It is also much more accurate for small 

 quantities to dispense with filters in collecting precipitates, provid- 

 ed the experimenter be not pressed in point of time. To manage 

 without these, the precipitate should be allowed to subside com- 

 pletely, the clear liquid above it be run off by a small syphon, dis- 

 tilled water put in its place, agitated, allowed to become clear, again 

 run off ; and this be repeated till the washing from soluble saline 

 matter be judged complete. The sediment is then transferred into a 

 small procelain capsule or platina crucible, carefully washing the last 

 portions out of the glass, allowed to repose a sufficient time, the 

 clear liquid above removed by a pipette, the moisture evaporated, the 

 precipitate heated to faint redness and weighed, deducting the tare 

 of the little vessel containing it. 



Should a speedy result be desired, filtering may be employed, 

 washing the precipitate on the filter with distilled water by a 

 pipette. The thick spongy paper with a rough surface, usually sold 

 as filtering paper, is unsuitable for this, because a very appreciable 



