Therefore,
(3.25 x 100 x 761 x .6272)/(801.78 x.1048) = 18.46 per cent. N. Theory = 18.50 per cent.
Professor Lungé has devised another form of nitrometer (Fig. 42), very useful in the nitrogen determination in explosives. It consists of a measuring tube, which is widened out in the middle to a bulb, and is graduated above and below into 1/10 c.c. The capacity of the whole apparatus is 130 c.c.; that of each portion of the tube being 30 c.c., and of the bulb 70 c.c. The upper portion of the graduated tube serves to measure small volumes of gas, whilst larger volumes are read off on the lower part.
[Illustration: FIG. 42. FIG. 43. SOME NEW FORMS OF NITROMETER.]
F.M. Horn (Zeitschrift für angewandte Chemie, 1892, p. 358) has devised a form of nitrometer (Fig. 43) which he has found especially useful in the examination of smokeless powders. The tap H is provided with a wide bore through which a weighed quantity of the powder is dropped bodily into the bulb K. From 4 to 5 c.c. of sulphuric acid which has been heated to 30° C. are then added through the funnel T, the tap H being immediately closed. When the powder has dissolved—a process which may be hastened by warming the bulb very carefully—the thick solution is drawn into the nitrometer tube N, and the bulb rinsed several times with fresh acid, after which operation the analysis is proceeded with in the usual way.
Dr Lungé's method of using a separate nitrometer in which to measure the NO gas evolved to the one in which the reaction has taken place, the gas being transferred from the one to the other by joining them by means of indiarubber tubing, and then driving the gas over by raising the pressure tube of the one containing the gas, the taps being open, I have found to be a great improvement.
1 c.c. NO gas at 0° and 760 mm.
Equals 0.6272 milligrammes (N) nitrogen.
" 1.343 " nitric oxide.
" 2.820 " (HNO_{3}) nitric acid.
" 3.805 " (NaNO_{3}) sodium nitrate.
" 4.523 " (KNO_{3}) potassium nitrate.
~Champion and Pellet's Method.~—This method is now very little used. It is based upon the fact that when nitro-cellulose is boiled with ferrous chloride and hydrochloric acid, all the nitrogen is disengaged as nitric oxide (NO). It is performed as follows:—A vacuum is made in a flask, fitted with a funnel tube, with a glass stopper on the tube; a delivery tube that can also be closed, and which dips under a solution of caustic soda contained in a trough, and the end placed under a graduated tube, also full of caustic soda. From 0.12 to 0.16 grm. cotton dissolved in 5 to 6 c.c. of sulphuric acid is allowed to flow into the flask, which contains the ferrous chloride and hydrochloric acid, and in which a vacuum has been formed by boiling, and then closing the taps. The solution is then heated, the taps on the delivery tube opened, and the end placed under the collecting tube, and the NO evolved collected. The NO gas is not evolved until the solution has become somewhat concentrated. Eder substituted a solution of ferrous sulphate in HCl for ferrous chloride. Care must be taken that the flask used is strong enough to stand the pressure, or it will burst.
The same chemists (Compt. Rendus, lxxxiii. 707) also devised the following method for determining the NO_{2} in nitro-glycerine:—A known quantity of a solution of ferrous sulphate of previously ascertained reducing power is placed in a flask, acidified with hydrochloric acid, and its surface covered with a layer of petroleum oil. About .5 grm. of the nitro-glycerine is then introduced, and the flask heated on the water bath. When the sample is completely decomposed, the liquid is heated to boiling to remove nitric oxide, and the excess of ferrous sulphate ascertained by titration with standard permanganate; 56 of iron (Fe) oxidised by the sample correspond to 23 of NO_{2} in the sample of nitro-glycerine.
~The Schultze-Tieman Method~ for determining nitrogen in nitro-explosives, especially nitro-cellulose and nitro-glycerine.—The figure (No. 44) shows the general arrangement of the apparatus. I am indebted for the following description of the method of working it to my friend, Mr William Bate, of Hayle. To fill the apparatus with the soda solution, the gas burette is put on the indiarubber stopper of basin W, and firmly clamped down. Then the taps A and C are opened, and B closed. When the burette is filled with soda solution half-way up the funnel Y, A and C are closed, and B opened. The arrows show the inlet and outlet for the cooling water that is kept running through the water jacket round the nitrometer tube. To collect the gas, raise the nitrometer off the rubber stopper, and place the gas tube from the decomposition apparatus in the glass dish W and under the opening of the nitrometer.