44 2 AGRICULTURAL ANALYSIS 



a way as to be fixed at any required altitude. It is filled with 

 water and connected by a rubber tube to the cooling tube D. 

 Within the cooling tube there is a graduated cylinder open at its 

 lower end. Its upper end is connected directly with the apparatus 

 C. The cooling tube D has a small side tube c near its upper 

 end, by means of which the air can enter or escape when the 

 position of A is changed. The apparatus C, in which the reaction 

 takes place, is a glass cylinder. Its upper end is continuous with 

 the T-tube provided with the stop-cocks a and b. One arm of 

 the T permits connection with the graduated measuring tube by 

 means of a rubber union. The lower end of C is closed with a 

 large hollow ground-glass stopper, carrying a small receptacle 

 within, so that it forms two separate water-tight compartments, 

 open at the top. 



The sodium amalgam is prepared as follows : 



In a clay crucible are heated 400 grams of mercury, and, 

 little by little, with constant stirring, four grams of dry sodium 

 are added. When cold, the amalgam is placed in a burette, hav- 

 ing a ground-glass stopper, and covered with petroleum. The 

 strength of the amalgam is established in the following manner. 

 A small glass thimble, ground even at the top, is filled with the 

 amalgam and struck off even with a ground-glass straight edge. 

 In this way the same quantity of amalgam is taken for each test. 

 This measured portion of the amalgam is placed in the inner ves- 

 sel of the glass stopper to C. Ten cubic centimeters of water, con- 

 taining 60 centigrams of tartaric acid, are placed on the outer ring 

 of the glass stopper, which is then inserted, well oiled, in C, clos- 

 ing it air- and water-tight. The tartaric acid solution also carries 

 a piece of litmus paper, so that its constant acidity may be in- 

 sured. The vessel A is fixed in a position which brings the water 

 in the graduated burette and tube D exactly to the o mark. The 

 cock a is closed, b opened, and C is inverted until all the amalgam 

 is poured into the solution of tartaric acid. The evolved hydro- 

 gen mixed with the air contained in the apparatus, is passed into 

 the graduated burette. After 15 minutes, the reaction is ended. 

 The water level within and without the graduated tube is restored 



