54 METHODS OF QUANTITATIVE ANALYSIS. 



The cover, provided with a gas inlet tube (Rose crucible), 

 is then put on and hydrogen gas passed in until all of the 

 air is displaced. Finally ignite for fifteen minutes in an 

 atmosphere of hydrogen. By this means the copper ox- 

 ide is converted into copper sulphide and is weighed as 

 such. From this weight the known weight of filter ash 

 is deducted and the percentage of lactose calculated from 

 the accompanying table. 



Instead of converting the cuprous oxide into copper 

 sulphide it may be reduced to metallic copper by heating 

 in an atmosphere of hydrogen and weighing the resulting 

 copper. Or instead of this the precipitated cuprous ox- 

 ide may be collected on a filter previously dried and 

 weighed and dried at loo degrees to constant weight. 

 The increase in weight of the filter will indicate the amount 

 of cuprous oxide. A still more simple process is to ignite 

 the filter and contents in a crucible as described above 

 and moisten with a few drops of cone, nitric acid. The 

 acid is then carefully evaporated off and the copper ni- 

 trate which is formed decomposed by ignition. From the 

 weight of black cupric oxide thus obtained the amount of 

 milk sugar may be calculated. For very exact determina- 

 tion the cuprous oxide should always be ignited in an 

 atmosphere of pure hydrogen and weighed either as 

 copper sulphide or metallic copper. For the calcula- 

 tion, find that number in the accompanying table which 

 is nearest to but less than the number for the copper 

 sulphide or metallic copper found. Subtract this from 

 the number found and multiply the remainder by the 

 corresponding factor, as given, and add to the result the 

 number for lactose given in the table. For example as- 

 sume the weight of metallic Copper obtained to be 0.2046 

 grams. The number in the table nearest to and less than 

 this is 0.2040 grams. The lactose equivalent is O.150 

 grams and the corresponding factor is 0.78. Then from 



