FRENCH AGRICULTURAL METHOD 395 



about two minutes until the air is completely driven out of all 

 the connections. The current is arrested for a moment by pinch- 

 ing the rubber tube which conducts the carbon dioxid into the 

 retort, and the vessel which is to receive the gas is then placed 

 over the delivery tube, this vessel being filled with mercury and 

 a strong solution of potash. The communication between the 

 retort and the carbon dioxid flask is broken and the flask is 

 heated slightly by means of a small lamp. The first bubbles of 

 gas evolved should be entirely absorbed by the potash. This will 

 be an indication of the complete absence of the air. When the 

 liquid is in a state of ebullition the nitrogen dioxid is set free. 

 The boiling is regulated in such a way that the evolution is reg- 

 ular and the liquid of the retort may not, by a too violent boiling, 

 pass into the receiver. The boiling is continued until the larger 

 part of the liquid is distilled and only three or four cubic centi- 

 meters remain in the retort. At this time a few bubbles of carbon 

 dioxid are allowed to flow through in order to cause to pass into 

 the receiver the last traces of nitric oxid. The gas received is left 

 for some minutes in contact with the potash. 



Afterward, in a small flask, G, the neck of which is drawn out 

 to a fine point, and carrying a bulb-tube, H, and a piece of rub- 

 ber tubing, there are boiled 25 or 30 cubic centimeters of water 

 for five or six minutes in order to drive all the air out of the 

 flask, and while the boiling is continued the rubber tubing is 

 fastened to the drawn-out part of the jar containing the nitric 

 oxid. Within the rubber tubing the drawn-out point is broken 

 and the vapor of water is forced into the jar and drives before 

 it the solution of potash which has filled the capillary part of 

 the drawn-out tube. As soon as the point is broken, the boiling 

 of the flask is stopped and by its cooling the nitric oxid passes 

 into it. It is necessary to press the rubber tubing with the fingers 

 in order that the passage of the gas into the flask be not too rapid. 

 As the solution of potash rises in the bell-jar which contains the 

 nitric oxid near to the point where the rubber tubing covers its 

 drawn-out portion, the fingers are removed and a clamp put in 

 their place. There still remains a little nitric oxid in the flask, 

 and to drive this out it is necessary to introduce five or six cubic 



