THE APPARATUS.

A is an apparatus for the generation of carbon dioxide free from air, which will be explained hereafter.

B is a flask, having a capacity of 125 or 150 c.c., in which the nitrate is decomposed in the usual manner by means of ferrous chloride and hydrochloric acid.

C is a small tube for the condensation of the aqueous hydrochloric acid which distills over from B.

D is a Geissler bulb, containing a concentrated solution of potassium carbonate, to arrest any acid vapors coming from C.

E, E are two pieces of ordinary combustion tubing, having a length of about 650 or 700 mm., in which is placed the permanganate solution employed for the absorption of the nitric oxide.  Their open ends are provided with lips in order to facilitate the pouring of liquids from them, care being taken not to so distort the ends that rubber stoppers cannot be made to fit them tightly.  They are placed in a nearly horizontal position in order to diminish the pressure required to force the gases through the apparatus and thus lessen the danger of leakage through the rubber joints.

a is a tube through which the ferrous chloride and hydrochloric acid are introduced into B, as in the method of Tiemann-Schulze.

b serves for the introduction of carbon dioxide to expel the air before the decomposition of the nitrate, and the nitric oxide afterward.

c is an unbroken tube ending at the lower surface of the stopper in B, and at the bottom of C.

The rubber joint, d, is furnished with a Mohr and also a screw pinch cock.  The joints, e and f, are furnished with Mohr pinch cocks.  The rubber tubing upon these should be of the best quality, and must be carefully tied.

[Illustration:  DETERMINATION OF NITRIC ACID.]

THE SOLUTIONS.

In consequence of the large volume of the permanganate solution required for the complete absorption of the nitric oxide, we have found it advantageous to use three solutions instead of two.

1.  A solution of permanganate such that one c.c. is equivalent to about fifteen milligrammes of nitrate of potassium, according to the reaction: 

  KMnO_{4} + NO = KNO_{3} + MnO_{2}.

This solution is employed for the absorption of the nitric oxide.  Its strength need not be exactly known.  There is no objection to a more concentrated solution, except that which pertains to all strong standard solutions, namely, that a small error in measurement would then give a larger error in the results. 100 c.c. of this solution are required for each determination, and the measurement is always made in one and the same 100 c.c. measuring flask, which, if necessary, should be labeled to distinguish it from that used for solution No. 2.

2.  A solution of oxalic acid which is very slightly stronger than that of the permanganate just described—­that is, a solution such that one c.c. of it will somewhat more than decompose one c.c. of the permanganate, according to the reaction: