OF ARTS AND SCIENCES : JANUARY 31, 1866. 93 



Before proceeding further with these somewhat random experiments, 

 it was deemed advisable to determine the temperature at which chloride 

 of copper begins to give off chlorine, in order to know how far it 

 would be safe to raise the temperature of the air-bath in conducting 

 an analysis. By making use of the air-bath to regulate the tempera- 

 ture of the chloride of copper, this determination was easily made. 

 During the heating of the chloride, a current of air from the air-gasom- 

 eter was admitted through the tube in which it was contained. 



Observations. — At 243°, not a perceptible trace of chlorine was 

 given off. After the lapse of fifteen minutes, at 250°, the nitrate of 

 silver, into which the gas was conducted, was observed to be slightly 

 milky ; this may, therefore, be taken as about the temperature at which 

 chloride of copper begins to suffer decomposition. At 267°, a solution 

 of nitrate of silver was instantly precipitated. 



Thinking that perhaps the small quantity of chlorine evolved under 

 these circumstances might be taken up again and retained if oxide of 

 copper were present, and possibly, also, that in that case a higher tem- 

 perature might be safely employed, — to make the conditions of the 

 experiment conform in this particular to those which exist in an analy- 

 sis, all but one inch of the chloride of copper was removed from the 

 tube, and in its place was put a mixture of asbestos and oxide of cop- 

 per, occupying a space of four inches in length, forward of the chloride. 

 The experiment was then repeated. Prolonged heating in a current of 

 air, and afterwards in oxygen, during which the thermometer rose to 

 350°, produced no reaction with nitrate of silver. From this it ap- 

 pears that the chlorine, which is given off below this temperature from 

 chloride of copper, when this is mixed with oxide of copper, is absorbed 

 and retained by the latter ; hence, that so high a temperature as 350° 

 may be safely employed for the air-bath in conducting an analysis by 

 this process. 



Analysis 1. — In this analysis the oxide of copper employed was 

 prepared in the ordinary way and strongly ignited. The space in the 

 tube occupied by the mixture of asbestos and oxide of copper was five 

 inches in length, and contained just five grammes of the oxide. Dur- 

 ing the experiment, the temperature of the air-bath was maintained at 

 about 350°. At the close of the combustion there was no appearance 

 of chloride of copper, except in the first half-inch at the back end of the 

 column of the mixture of oxide of copper and asbestos ; showing that 

 the temperature employed was favorable for rapid and complete absorp- 

 tion of the chlorine. 



