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: 2KMnO_{4} + 3H_{2}SO_{4} + 5C_{2}H_{2}O_{4}.2H_{2}O = K_{2}SO_{4} + 2MnSO_{4} + 18H_{2}O + 10CO_{2}. The exact strength of this solution need not be known, since we only require the difference in value between it and solution No. 1, which is determined by means of solution No. 3. 100 c.c. of this solution are also required for each determination, and the measurement, as in the preceding case, is always made in the same 100 c.c. measuring flask. 3. A dilute, carefully standardized solution of permanganate of potassium. The method of using these solutions is as follows: 100 c.c. of No. 1 and No. 2 are measured off (each solution in its own measuring flask), brought together in a covered beaker glass, and acidified with dilute sulphuric acid. The excess of oxalic acid is then determined by means of solution No. 3. When it is desired to make a determination of nitric acid, 100 c.c. of solution No. 1 are measured off, and as much of it as may be convenient is poured into the tubes, E, E, together with about a gramme of zinc sulphate for each tube, which substance appears to considerably facilitate the absorption of the nitric oxide by the permanganate. When the operation is over, the contents of E, E are poured into a beaker glass. 100 c.c. of solution No. 2 are then measured off, and a portion, together with a little sulphuric acid, poured into E, E, to dissolve the oxide of manganese which has separated during the absorption of the nitric oxide. The oxide having been dissolved, the liquid in E, E, and the rinsings of the tubes, also the residues of permanganate and oxalic acid left in the measuring flasks, and the rinsings from these, are all brought together in the same beaker glass. Finally, the amount of solution No. 3 required to decompose the excess of oxalic acid is determined. If we subtract from the amount thus found the quantity of permanganate required to equalize solutions Nos. 1 and 2 (previously ascertained), we shall have the amount of permanganate actually reduced by the nitric oxide, according to the reaction: 6KMnO_{4} + 10NO = 3K_{2}O + 6MnO + 5N_{2}O_{5};