THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
310
The oxides of nitrogen in the aspirator bottle are determined in the way customarily employed. Through the stopcock D are run successively 5 cc. hydrogen peroxide, 5 cc. water and, if necessary, approximately 10 cc. oxygen. The bottle is shaken and, after the oxides haec largely been absorbed, an excess of 0 . 1 N alkali is added. The bottle is again shaken and allowed to stand until all oxides are absorbed. It is then rinsed out and the excess alkali titrated with standard acid.
COMPUTATION OF ANALYSIS AT POINT OF SAYPLIKG Case i-All Components Gaseous and No Mist Present The eauivalent cc. of alkali neutralized by the gas passed through the absorber and the gas in the aspirator bottle and the permanganate used are computed, and the calculationsa made as follows: A = Cc. 0 1N alkali neutralized by nitrogen oxides in absorber. P = Cc. 0.1 N permanganate used to oxidize nitrite in absorber. (3A P) = Cc. 0 . 1 N alkali neutralized by NOz. C = D = Total alkali- C = Cc. 0 . 1 N alkali neutralized by NO. E = C/4 = Per cent by volume of NOz in gas.7 F = D/4 = Per cent by volume of NO in gas. E F = Total oxides present. E 100 x -= Percentage oxidation of nitrous gases in terms F: + F OF NO*. The composition of the nitrous gases as above computed represents that which i t would have were all components completely gasified. Such conditions obtain when the temperature of the gas a t the point of sampling is above the dew point and no fog or mist exists. A subsidiary case may be encountered occasionally when the and NO2, N O being completely gas consists entirely of "03 absent. If this be met with, the percentage oxidation is over 100 per cent. Under these conditions the components are determined by the relationships : Total NO? = 2 X Total nitrite in Alkali I Total "03 = Alkali I Alkali I1 - Total NO1
+
+
+
Case 9-Mist Present i n Gas Line and Temperature of Gas a t Point of Sampling Approximately That of Alkali Absorber (NO in excess over NOa)
From a consideration of Reactions I1 and I11 and the reaction HNOl (mist) NaOH = NaNOs -HzO l
+
6
BASIS OF CALCUL.4rION NO1 reacling according to Equation I = 3/2 Alkali I NO, reacting according t o Equation I1 = 1/2 nitrite Total NOz = 3/2 Alkali I 1/2 nitrite NO = Alkali I Alkali I1 total WOz If 0 . 1 N solutions are used Permanganate titration Total NOS = 3/2 Alkali I 4-
+
+
and bearing in mind that any excess NO will escape from t h e first alkali solution, the following identities may be written : Total
mist = Nitrate present in Alkali I = Alkali I-Nitrite in I Total NOZ = Nitrite in I 2
"03
Total NO = Nitrite in I 2 For 0 . 1 N solution these become Total HNOa mist = Alkali I
+ Alkali I1
- Permanganate 2
Total NOz = Permanganate 4
+
Permanganate Alkali I1 Total NO = 4 The percentages by volume of the constituents are computed in the same way as for Case 1. The percentage oxidation is given by the expression: Per cent "03
X 2 . 5 iper cent NOZ X 2
+ per cent N O -
Total percentage CORRECTION FOR OXIDATIOA I N
TRANSIT
The composition of bhe gas as calculated represents that at the moment of reaching the alkali, and consequently for a mixture containing excess oxygen does not represent the composition in the pipe at the point of sampling but at a point somewhat further along the pipe. From a knowledge of the rate of oxidation of NO it is poPsible to compute the romposition at, any point along the pipe line provided the rates of flow are known. For dilute gas mixtures containing less than 5 per cent excess oxygen, a correction for the oxidation taking place in the sample tube and gas analysis apparatus is in general unnecessary. In case, however, the diluent gas is air, the correction must be made. The complete equation4 for the rate of oxidation of NO is:
where CO= Concentration of oxygen a t timet = 0 (mol. fraction). C1=Concentration of nitric oxide a t time t = 0. C = Concentration of nitric oxide a t time t = t.
When oxygen in considerable excess is present the equation may be simplified into
-
2
-
Vol. 14, No. 4
3 Alkali titration
+ Permanganate titration
which is quite accurate enough for calculating the correction term.
2
The numbct of mole.; of nitrogen peroxide absorbed iii alkali is equal t o the number of equivalents of alkali neutralized by nitrogen peroxide, or 7
"
-.L
Cadmium in 1921
*7 = 0 . 9 8 atm. The volume is one liter and the temperature is, therefore, 760 about 2 j 0 C . , or 298O Abs. The number of moles of inert gas is then given PV 0.98 x 1.0 = 0.04 mole. by the solution n = = RT 0.0821 X 298 C C The percentaxe of NOz is therefore 100 X loooo o,04 and D The variations correspondingly the percentage of NO is found to be -
Figures obtained from producers by the United States Geological Survey show that the total production of metallic cadmium in 1921 was 65,101 lbs., a decrease of 64,182 lbs., or about 50 per cent, as compared with the production in 1920. On the other hand, the production of cadmium sulfide in 1921 amounted to 65,446 lbs., an increase of 33,313 lbs., or more than 100 per cent, over the production in 1920. The value of the metallic cadmium produced was $63,799 and that of the cadmium sulfide was $71,336, making a total value of $135,135, as compared with $188,535 in 1920, a loss of 28 per cent. The average selling price of metallic cadmium in 1921 was 98 cents a pound, as against $1.17 in 1920, and that of cadmium sulfide was $1.09 a pound, as against $1.16 in 1920. A noteworthy development of the year was the extension of the use of cadmium electroplating for preventing rust.
in temperature and pressure which will be found in the gas in the aspirator bottle are not enough t o influence appreciably the calculated percentages of NOz and NO. Of course, if the volume aspirated is other than one liter, the proper factor must be calculated. For a volume of 1.16 liters the factor is 4 0 .
The University of West Virginia is having plans prepared forthe erection of a new chemical laboratory, estimated to cost about. $400,000.
10000 T h e number of moles of inert gas in the aspirator bottle is calculated from the equntion p v = nKT. The pressure (as a result of observation) has been found to averaxe closely 1.6 cm. Hg vacuum (corresponding to the height of liquid in ;he absorption bulb). Therprrssure is, therefore,
-
- -
4
.
