ANALYSIS OF COMPLEX MATTER 127 



repeating the process, after the addition of water, a sufficient 

 number of times. The silver is thus washed, and if time be 

 allowed for settling before each decantation, none need pass to 

 the filter paper. If it does, it may be made to return to the 

 crucible by a stream of water, or by burning the dried paper 

 over the crucible. The silver in the crucible is now carefully 

 dried, and finally raised to a red heat ; it is then cooled and 

 weighed. 



In much the same way the equivalent quantities of iron 

 and copper are determined. A small quantity of pure iron 

 wire is weighed in a porcelain crucible of known mass. Add 

 to this a warm solution of copper sulphate. After they have 

 been in contact for some time, break up the copper with a 

 glass rod, so that any unchanged portion of the iron may come 

 in contact with the solution, and then warm gently. The 

 copper which is formed is washed by the addition of water 

 and frequent decantation. It is then dried carefully over a 

 water-bath, as it undergoes change when raised to a high tem- 

 perature in the air. The crucible is then dried and weighed. 

 84. The Relative Quantities of Chemically Reacting 

 Matter, Equal Quantities of Magnesium and Aluminium 

 set free from Hydrogen Sulphate different Volumes of Gas 

 at the same Temperature and Pressure ; but there is a Con- 

 stant Ratio between these Volumes, and this Ratio is main- 

 tained when the Gas is liberated from Hydrogen Chloride. 

 A small quantity of magnesium is weighed, and a mass of 

 aluminium is made equal to it. Two graduated tubes are filled 

 with water, and supported in a vessel of water. The equal 

 quantities of the two metals are placed at the bottom of the 

 vessel, directly under the tubes, which are then brought very 

 near to the bottom of the vessel. Hydrogen sulphate is now 

 added, and by diffusion through the water it reaches the 

 metals. Gas is observed to be liberated. If the quantity is 

 too great to be collected in the tubes, smaller quantities of the 

 magnesium and aluminium will need to be taken. Before 

 measuring the relative volumes of the gas, it is necessary that 

 they should be in exactly the same condition. They will be 

 in the same condition with regard to temperatures, and will 



