Determination of Nitrous Oxide KELSO B. MORRIS AND ETHEL M. DAVIDSON Howard University, Washington, D . C.
1" THE course of oxidation studiesunder an OfficeofNsvalResearch contract, it became necessary to determine nitrous oxide, a product of the reaction. The authors elected to use two wellknown methods-slow combustion and catalytic reduction-in obtaining data on nitrous oxide and nitrous oxide-nitrogen mixtures. The chemical equation that represents the reaction in both methods is
in which the total contraction is equal to the volume of nitrous oxide. Kobe and MacDonald (1) employed with success a commercial silica gel catalyst containing 0.125% of platinum and reported that nitrous oxide may be reduced o v ~ rthe catalyst by a limited excess of hydrogen a t 515' C. A special Burrell Build-Up gas analysis unit containing slowcombustion and catalytic oxidation (or reduotion) assemblies was used in the work. The latter assembly provides for heating of the catalyst tube by means of a Perme. Therm heater (Burrell Teohnicd Supply Co., Pittsburgh, Pa.). The manufacturer states that the heater is adjusted to operate at any point between 500' and ,525' C. and the maximum variation over a range of 105 to 125 volts is *2.5- C. The manufacturer, though not willing to re-
lease data an the catalyst, asserts that its activity differs from that of Kobe and other previous catalysts. The volume of hydrogen used was from 2 to 2.5 times the volume of nitrous oxide in the sample. One double pass a t the rate of 4 to 5 ml. per minute was the procedure adopted for the slowcombustion pipet. For the catalyst tube, the method involved three double passes a t 25 ml. per minute. Data. show that the commercially available crttdyst tube and heater are convenient and satisfactory for the determination of nitrous oxide, and indicate practically the same order of accuracy for the two methods. One and three double passes, respectively, a t the flow rates indicated, are satisfactory for the slow-combustion technique and the catalyst tube. For the same volume of gas passed, the catalyst tube is faster. Thus, the minimum handling time for 50 ml. of gas would he 20 to 25 minutes in the slow-oombustion analysis a6 compared with 12 minutes with the catalyst tube. Traces of ammonia were noticed oocasionally where the slow-combustion pipet had been used, but never where use had been made of the catalyst tube. LITERATURE CITED
( 1 ) Kobe, K. A,, and MacDonald, R. A.. IND. ENG.CHEM..ANAL. RPOElY
ptobenzot
y ! ,,yf2a C
P
solution. The commercial samples usually contain considerahle ammoniu m chloride, which should be r,emoved by extraction using vt?ry slightly alkaline solutions.
~
/
~ - I Y I ~ ~ - l i ~ ~ ~ " D e nISe O very ~ n mmeui& , ~ ~ ~ , ~GO
crystaiiize ana no orystds except from the melt apparently ever show reproducible and definite interfacial angles. The best crystals obtained for this study were obtained hy slow evaporation of a chloroform or
aI
\
CRYSTAL MoRPHoLoGY ( d e termined by W. C. Mc100
Crone). Crystal System. Monoclinic. Fqrm- and Habit. Crystals obt,ained from chloroform were long flat rods showing basal inacoid [ 001 1 ; orthopinaooid 100); andprisms (210). The interfacial angles vary by as much as 10" from crystal t o crystal and even on the same crystal; many feces a m curved. A x i a l R a t i o . a:h:e =
(y 1 : -
'4
\,
I
~:
7'\toe-
2.655: 1: 1.335.
Figure% Orthographic Pmjeetion of Typical Crystal of Z-Mersaptobenzothiazole
Figure 1.. 2-Meroaptoben.othiazole Left. C w s t d s from chloroform and xylene Right. Fusion preperstion ahowing charaoteristio shrinkege
157
Interfacial Angles (Polar).
210 A 210 = 77".
Bets. .4ngle. 109'. Cleavage. 010, 100.
