S. L. Penfield — Methods for Determination of Water. 31 



merited upon, the ease with which the water is given off and 

 the necessity of adding some substance in order to retain a 

 volatile constituent. A simple hard glass tube closed at one 

 end, of about 6 mm internal diameter and 20-25 cra long can often 



be used, while some of the forms that have been found more 

 convenient are represented in figures 1 to 3.* Number 3 may 

 be drawn out from ordinary combustion tubing. These tubes 

 must be thoroughly dried inside, which is best accomplished 

 by heating and aspirating a current of air through them by 

 means of a glass tube reaching to the bottom. This is a neces- 

 sary precaution and should always be taken even if the 

 tubes are apparently dry. In order to bring a weighed quan- 

 tity of the substance into the lower end of a tube without 

 depositing any of the material on the sides, a thistle tube, fig. 

 4, is employed. This is conveniently cleaned by drawing 

 through it a bit of dry cotton attached to a fine wire. 



For heating, a Bunsen burner or blast lamp flame may be used, 

 according to the temperature required. The water that is ex- 

 pelled condenses in the cold part of the tube, but cannot escape 

 as there is no outward current to carry it along, except a very 

 slight one caused by the expansion of the air when the tube is 

 first heated. To guard against any possible circulation of cur- 

 rents of air however, which might carry off traces of water, a 

 short piece of glass tube drawn out to a capillary, fig. 5, is 

 joined on by a rubber and is removed before 

 weighing. While being heated, the tube may 

 be held by a clamp or in the hand, and if the 

 quantity of water is considerable it should be 

 expelled slowly and driven up into the first bulb, figs. 2 and 3, 

 to prevent its flowing back upon the hot glass. To prevent 



* In making the ignition tubes considerable time may be saved by fusing new 

 bottoms on to those that have previously been used. 



