452 AGRICULTURAL ANALYSIS 



with from eight to 10 cubic centimeters of water, are sucked in- 

 to the geissler bulbs while the glass in the tower E is also thor- 

 oughly moistened with the iodid. The geissler bulbs should be so 

 arranged that gas bubbles through only the 'last of them, the 

 liquid in the others remaining quiescent. 



All the joints having been made tight the carbon dioxid is 

 turned on briskly and passed through the apparatus until a 

 small tubeful collected at /, over caustic potash solution, shows 

 that no appreciable amount of air is left in it. The small outlet 

 tube / is replaced by a tube, filled with broken glass which has 

 been moistened with the above-mentioned iodid solution, and 

 closed by a cork through which an outlet tube passes, the object 

 of this trap tube being to prevent any air getting back into the 

 apparatus. The brisk current of carbon dioxid is continued for a 

 minute or two longer, so as to practically expel v all the air from 

 this last tube. The stream of gas is now stopped for an instant, 

 and about 15 cubic centimeters of pure concentrated hydrochloric 

 acid, free from chlorin, run into A through the funnel g (into 

 the tube of which it is well to have run a few drops of water 

 before beginning to expel the air from the apparatus), and A is 

 shaken so as to mix its contents thoroughly. A slow current of 

 carbon dioxid is again turned on (one to two bubbles through the 

 wash-bottle per second), and A is gently warmed over a burner. 

 It is a distinct advantage that the reaction does not begin until 

 the mixed solutions are warmed, when the liquid becomes orange- 

 colored, the color again disappearing after the nitrosyl chlorid 

 and chlorin have been expelled. The warming is very gentle 

 at first in order to make sure of the conversion of all the nitric 

 acid, and also because the first escaping vapors are relatively very 

 rich in chlorin; afterwards the liquid in A is briskly boiled. A 

 very little practice enables the operator to judge as to the proper 

 rate of warming. When the volume of liquid in A has been re- 

 duced to about seven cubic centimeters (by which time it is again 

 colorless), the stream of carbon dioxid is slightly quickened and 

 the apparatus allowed to cool a little. The burner is now set 

 aside for a few minutes, and two cubic centimeters more of hydro- 

 chloric acid, previously warmed in a test-tube, run in gently 



