134 ELEMENTS OF LABORATORY WORK 



of observation may be found. A litre contains 1,000 cubic centi- 

 metres. All the necessary data are now ready for calculation. 

 88. The Measurement of the Quantity of Oxygen evolved 

 by heating a given Quantity of Silver lodate, and also of the 

 Density of Oxygen. A weighed quantity of silver iodate is 

 heated in a small tube A of hard glass, connected with a 



vessel as shown below. As the 

 oxygen is evolved, it displaces 

 from the vessel B a correspond- 

 ing volume of water, which is 

 collected in a graduated vessel c. 

 The loss of matter from A, when 

 the change is complete, gives 

 the quantity of oxygen pre- 

 viously contained, and also the 

 weight of oxygen contained 

 in a measurable volume. 



The corks must fit the tubes and vessels so as to be 

 perfectly air-tight. The tube must be gradually raised in tem- 

 perature by a Bunsen flame, allowed to remain at a moderate 

 temperature for some minutes, and then allowed to cool to the 

 temperature of the room. The water in the graduated vessel 

 is brought to the same level as that in the aspirator. We know 

 then that the pressure within the apparatus is the same as that of 

 the atmosphere, which may be ascertained from the barometer. 

 The volume of water in the graduated vessel will equal the 

 volume of gas given off from A. Its temperature and pressure 

 are known, and the quantity of water- vapour which will be 

 mixed with it at the observed temperature is given in the table 

 on page 110. The loss of matter found from weighing A will be 

 equal to the quantity of matter contained in this volume of gas, 

 and hence the density may be found. 



The density may also be measured by means of the atmo- 

 spheric pressure forcing back the oxygen from the vessel B 

 into a vacuous flask which has been put in the place of A. 

 From this flask all the air has been expelled by steam, as 

 described in the previous experiment, and it has been accu- 

 rately weighed. It is connected with the vessel B, and the 



