4OO AGRICULTURAL ANALYSIS 



,ter, mounted and connected as shown in the illustration. The 

 delivery tube dips into a jar of mercury in a trough containing 

 the same liquid. The long supply funnel-tube a is of small 

 bore, holding in all only one-half cubic centimeter. The con- 

 necting tube, F, carrying a clamp, is also of small diameter and 

 serves to connect the apparatus with a supply of carbon dioxid. 



In practice, the supply tube a is first filled with strong hydro- 

 chloric acid and carbon dioxid passed through the apparatus un- 

 til the air is all .expelled. This is indicated when a portion of the 

 gas collected over the mercury, is entirely absorbed by caustic 

 alkali. 



At this point the current of carbon dioxid is stopped by the 

 clamp C, and a bath of calcium chlorid, B, heated to 140 is 

 brought under the bulb A, until the latter is half immersed 

 therein. The temperature of the bath is maintained by a lamp. 

 By allowing a few drops of hydrochloric acid to enter the receiver, 

 the carbon dioxid is almost wholly expelled. The end of the 

 delivery tube is then connected with the tube, T, filled with 

 mercury, and the apparatus is ready for use. 



The nitrate, in which the nitric acid is to be determined, in a 

 dry state, is dissolved in two cubic centimeters of the ferrous 

 chlorid solution (one gram of iron in 10 cubic centimeters), one 

 cubic centimeter of strong hydrochloric acid is added, and the 

 whole is then introduced into the receiver through the supply- 

 tube, being followed by successive rinsings \vith hydrochloric 

 acid, each rinsing not exceeding one-half cubic centimeter. The 

 contents of the receiver are, in a few moments, boiled to dryness ; 

 a little carbon dioxid is admitted before dryness is reached, and 

 again afterwards to drive over all remains of nitric oxid. In 

 the recovered gas the carbon dioxid is first absorbed by caustic 

 potash, and afterwards the nitric oxid by ferrous chlorid. All 

 measurements of the gas are made in Frankland's modification 

 of Regnault's apparatus. The carbon dioxid should be as free 

 as possible from oxygen. The carbon dioxid generator is formed 

 of two vessels, the lower one consisting of a bottle with a tubule 

 in the side near the bottom ; this bottle is supported in an inverted 

 position and contains the marble from which the gas is generated. 



