454 Penjield and Bradley — Precipitates o?i Asbestos. 



A large fragment is used to close the throat of the filter tube, 

 and on this is placed a layer of powdered quartz about six or 

 eight times as coarse as sea sand, from which fine material has 

 been carefully removed by screening and washing. In order 

 to deposit a uniform layer of asbestos on the quartz, it is 

 recommended to observe the following precautions : The bot- 

 tom of the filter tube is closed with the finger, and the tube is 

 half filled with water ; asbestos suspended in water is then 

 added, when upon removing the finger, it will settle in a 

 smooth layer upon the quartz, and may be firmly fixed by use 

 of a filter pump. The asbestos and precipitate collected on it 

 dry slowly in the tubes in an ordinary drying oven, but 

 removal of water may be quickly accomplished by drawing a 

 slow current of air through the tubes, the latter being heated 

 in an air bath, which may be improvised from a baking pow- 

 der can. Such filters may be found useful for collecting 

 many precipitates which need not be subjected to strong igni- 

 tion, silver chloride for example, and the}^ are especially 

 recommended for precipitates which are subsequently to be 

 ignited in gases, as will be illustrated by numerous examples. 

 They are admirably adapted for use with an extractor, where 

 either a precipitate collected on the asbestos, or a powder, is to 

 be treated with some solvent, such as either, carbon bisulphide 

 or alcohol. The arrangement of a filter tube in an extractor is 

 suggested by figure 3, where a is the neck of a flask containing 

 some solvent, the vapors of which pass up between the filter 

 tube and the outer jacket, and after condensation drop down 

 upon the material collected on the asbestos. At b there should 

 be some swelling of the tube to allow a free upward passage 

 of vapors. 



In case of a small amount of organic material being present, 

 it could undoubtedly be burned in the tube in oxygen gas and 

 the resulting carbon dioxide and water collected and weighed. 



Precipitates collected on the asbestos can be ignited by 

 applying a gentle heat to the tubes while supported in an 

 inclined position, or the following arrangement may be found 

 very serviceable : a small hole is pierced in the bottom of a 

 porcelain crucible and enlarged by chipping until a hole of 

 the desired diameter is obtained, through which is passed 

 the smaller part of the filter tube. The crucible not only 

 serves as a support for the tube, but also protects the glass 

 and precipitate from too strong ignition. A ring burner is 

 placed beneath the crucible, and so adjusted that the lower 

 part of the filter tube passes through the center of the burner, 

 and may by its lower end be connected to a gas generator. If 

 it is desired to increase the temperature of the upper part of 



