396 STATE BOARD OF AGRICULTURE. 



bottom by a stop-cock, (2) a delivery tube (D) and (3 )a 10 c.c. burette 

 (C). The stem of the cylinder which should be of capillary tubing, 

 reaches almost to the bottom of the bottle. The delivery tube is also 

 of capillary tubing of about 1-2 m.m. internal diameter, the upper end 

 being bent twice at right angles to connect with a gas burette (E) 

 while the lower end is flush with the bottom of the rubber stopper. This 

 tube should not extend above the top of the cylinder and should have 

 a three-way Geissler stopcock (K) near the middle. At fiirst an ordi- 

 nary gas burette was used for measuring the gas volumes and a Hempel 

 ])ipette (F) for the absorption of the nitric oxide. These two pieces of 

 apparatus Avere later combined into one piece (E), which served both 

 purposes. It consisted of a 10 c.c. pipette, to one end of which was 

 sealed a series of three bulbs, two of 35 c.c. capacity each and one of 

 about 150 c.c. The ends of this apparatus were closed by stopcocks, 

 a three-way horizontal one at the top and a straight one at the bottom. 

 A leveling bulb (L) was attached to the large bulb and filled with an 

 acid solution of potassium permanganate. In the course of a determina- 

 tion the mixture of gases was collected in this apparatus over the per- 

 manganate solution. At the end of the reaction both stopcocks were 

 closed and the gas shaken out in the large bulb, the lower stopcock 

 being opened occasionally to allow the liquid to run in and equalize 

 the pressure. This saves transferring the gas to the Hempel pipette 

 and back to the gas burette and the graduations of the 10 c.c. pipette 

 permit of a more accurate reading than do those of the ordinary gas 

 burette. As an acid permanganate solution liberates gaseous oxygen 

 on standing, several precautions must be taken to guard against error 

 from this source. This piece of apparatus can be used simply as a gas 

 burette in connection with a Hempel pipette as shown in the illustra- 

 tion. In this arrangement one branch of the three-way cock is con- 

 nected with the delivery tube and the other with the Hempel bulbs 

 which are filled with an alkaline permanganate solution. This solu- 

 tion contains 5 g. KMNO^ and 2.5 KOH per 100 g. H.O. and has the 

 advantage over the acid solution of being perfectly stable. The gas 

 volumes in this method cannot be read over it directly, however, as 

 the manganese dioxide which is precipitated renders accurate readings 

 difficult. On the whole however the use of the alkaline solution in 

 the Hempel apparatus seems to give the best results. 



By introducing the three-way cock instead of the ordinary straight 

 one into the delivery tube it becomes unnecessary to disconnect the 

 gas burette and delivery tube for each determination. This removes 

 one possible source of error in the introduction of air into the apparatus 

 in making this connection. Before starting a determination all air 

 should be driven out of that part of the apparatus between this three- 

 way cock and the Hempel bulbs. This can be accomplished by opening 

 the three-way cock between the gas burette and the Hempel bulbs and 

 lowering the leveling bulb. The permanganate solution will be drawn 

 over filling the connecting tube as far as this cock which can then be 

 turned so as to close this opening and open the one between the gas 

 burette and the delivery tube. By raising the leveling bulb the air can 

 be driven out through this outlet and the burette and delivery tube filled 

 with liquid as far as the cock (K) which should then be turned so as 

 to close the opening towards the gas burette. The cylinder (B) in- 



