Microdetermination of Carbon and Hydrogen by a Rapid Automatic Procedure moval. This method was developed to avoid direct handling of the tubes which we believed contributed to the blank. No effect on the blank was observed. The totalelapsed time for one analysis was reduced from 20 to 15 minutes by using a faster cycling period. However, the schedule proved too taxing on the analyst. ACKNOWLEDGMENT
The authors are grateful to Patricia
Gallant, Louise Porter, and Rudolf
START SWiTCd
Oeckinghaus for their assistance in
6LdS.S WOOL
LINE
Figure 1. furnace
Electrical diagram of circuit that controls movable
SIR: In a previous publication (3) the authors stated that the rapid determination of carbon and hydrogen could be adapted to an automatic apparatus. This communication describes the equipment necessary for such automatic combustions. The physical make-up of the combustion train is the same as published (3). The electrical circuit which controls the operation of the movable furnace is outlined in Figure 1. A reversible Hagen synchronous motor (1/6 r.p.m., Model 52-02164) is used. A Cramer 5minute automatic reset timer (Type 412E-5M, WD-1123) is represented as a circle in the figure. The micro limit
SILICA EEL / O - P O U € S H
avoid errors caused by a spent catalyst. The schedule of replacement, to a large extent, will depend on the type of compountls analyzed in each laboratory. The nitrogen oxide absorber described in the previous publication ($) was modified to hold a larger amount of catalyst. The design is similar to that of Belcher (1) and filled as seen in Figure 2. It is difficult to prepare manganese dioxide of reproducible activity. Although a good grade can be purchased (Laboratory Equipment Corp.), its capacity is limited to
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Figure 2.
DlOXlOE 1 0 - 2 0 Y S H
Nitrogen oxide absorber
r r \* I I 0
'0" RING
ILICONE
'0" R &
W
switches Limit switch are 1Honeywell is open when Type the BZ-2RS. movable furnace is in the standby position. The motor drive is actuated when the start switch is momentarily depressed. The furnace reaches limit switch 2 in 3 minutes and remains over the sample for the next 4 minutes. At the end of the seventh minute the timer reverses the direction of the furnace which moves back to limit switch 1. The automatic combustion procedure singled out a serious deficiency. Compounds exploded with greater frequency than was experienced in the manual operation. The problem was solved by replacing a 3- to 4cm. portion of the silver filling in the 550" C. fixed furnace (3) with silver-manganese dioxide catalyst (9). Good results were obtained, regartiless of the severity of the explosion, as long as the catalyst was active. The combustion tube is replaced each month or a t the completion of 500 analyses to
SCALE Icm
---
Figure 3.
Absorption tubes
approximately 70 analyses under our conditions. In an attempt to determine the origin of the blank previously described (S), the absorption tube was modified to provide a different method of coupling to the combustion train and is shown in Figure 3. The over-all dimensions of the tube were unchanged. The silicone rubber O-rings protruded 1 mm. beyond the glass edge and were cemented to the tube with an epoxy resin. The pliability of the silicone rings provides an airtight fitting with suitable pinch clamps. The tubes are conveniently handled with forceps in both positioning and re-
establishing the procedure and to M. R. Rarnos of Cramer Controls Corp. who helped develop the electrical circuit. P. E c k of Vienna, Austria, constructed the absorption and connecting tubes. LITERATURE CITED
(1) Belcher, R., I
~G., A&. ~
chirn. ~
~
,
Acfa 4,401 (1950). (2) KGakova, E.,Korbl, J., Chem. lis@ ~
3 ~ & I., ~ Jett, ~ L,~ M.,~Dorf~ man, L.,A ~ cHEM. ~ 30, ~ 132. (l9%).
&
Loms DORFMAN G. I. ROBERTSON CIBA pharmaceutical produ&, I,,~. Summit, N. J. VOL. 32, NO. 12, NOVEMBER 1960
0
1721
.
