ANALYSIS OF COMPLEX MATTER 



135 



clip slowly opened. At the same time the vessel c is raised, 

 so that the water in it may be at the same level as that in the 

 aspirator. We have now the flask filled with oxygen and 

 water- vapour, at a pressure of the atmosphere which is read by 

 the barometer, and at a temperature which is made to agree 

 with that of the room. The proportion of water-vapour for 

 this temperature is ascertained ; the flask is again weighed. 

 The increase of mass represents a certain volume of oxygen, 

 which is found by subtracting the volume of water from the 

 whole volume of the flask, and making allowance for the 

 water- vapour present. The density thus found should agree 

 with that found by the former calculations. 



It may be noted that inaccuracy will be caused by the 

 small quantity of air which is in the tube A 

 and the connecting tube at the commence- 

 ment of the operation. For this reason 

 they should be as small as possible. 



89. Analysis of Air by means of Phos- 

 phorus. A long graduated tube, with a 

 tap and nozzle at one end, is held upright, 

 with its open end under the level of water in 

 a vessel. An inverted burette answers the 

 purpose (fig. 46.) The level of the water 

 inside is made to agree with that outside the 

 tube, and then accurately read. A piece of 

 phosphorus, attached to the end of a copper 

 wire, is then pushed up about half-way 

 inside the tube. The phosphorus is allowed 

 to remain as long as the water rises within 

 the tube an action which will^ continue for 

 a day or more. It is then removed. The 

 pressure within the tube is again adjusted to 

 that of the atmosphere, and the volume of 

 gas remaining is ascertained. This space 

 will be filled by that portion of the air 

 which is not acted upon by phosphorus and by water- vapour, 

 the proportion of which may be ascertained from the table on 

 page 110. 



PHOSPHORUS 



