535
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 EXTERNAL BINDING POSTS FOR VOLTMETER
9 9
d
CHASSIS
CONNECTOR
I
SELECTOR SWITCH
1 8 9 10
12 BLOCK
I BATTERY #I
Figure 2.
j
#2
Wiring Diagram of External Hatter> Supplj for Beckniaii Spectrophotometer
for periodic disassembly of the apparatus to iefill the steam generator with water. It has been used by the authors successfully for several years.
A water inlet, A , connected to a three-way stopcock, R , is attached to the steam generator as shown in the diagram. Stopcock B is connected to the water line and to the condenser inlet, C. A straight adapter, D, is attached below the outlet, E , of the steam trap and connected to a length of tubing leading to the sink. The condenser outlet, F , is connected to a small piece of glasq tubing, G, slightly flattened a t one end, which is attached to D by means of a wire. I n use, B 19 normally turned bo as to let water flow through the condenser jacket. At the end of each determination, the stopcock is turned briefly in the other direction. This causes cold water to flow into the steam generator, which results in the immediate creation of the partial vacuum necessary to suck hack the -pent sample. At the same time, the steam generator has I i t w i it4illed with water for the next determination. The flame nrwt iiot tw removed, a t i t l boiling is not interruptpd too long.
:orrect values for terminals 1 through 10 are listed i i i this rr,rvic,ing bulletin (1). Voltage values for terminals 11 anti 12 Fliould read $20 volts and “slightly positive,” respectively. T(~rininal 3 is ‘rground” and the battery cabinet case can be Connected tn it for shielding. Figure 2 is a wiring diagram of the battery calmest 1 s described. The external C battery supply has been used routinely in this ;ahoratory with success. -is a result, the time required for diagnosing and eliminating instrumental t,roubles arising from ( ’ 3at tery failure has been materiallv reduced by this niodification. ACKNOWLEDGMENT
The authors wish to express their appreciation to T. P. Sord,quid, Hospitalman, United States S a v y , for his technical assistance. The opinions evpresscd ale the authors’, and do not necessarily reflect those of the S a w 1)epaitment LITER.ATURE CITED
(1 I Beckmai: Instrumrnts, l n c . . South Pasadena, Calif., BILZI.l W D , 8, August 1950.
(2 Reckman Instruments, Inc., Xational Technical Laboratories, I
South Pasadena, Calif., Bd1. 150-A, 10, Drawing No. CD25C, August 1946. ( 3 ) I t i d . , p. 11. Drawing S o . WD 2500 D. ‘4) Cecchini, L. P., ANAL.CHEM., 25, 547 (1953). .~.5) Schiller. A . A , and Cecchini, L. P., Naval Medical Research Institute Project SM 001 008, Rept. 2 (July 20. 1948).
Modification of Parnas-Wagner-Pregl Micro-Kjeldahl Apparatus. Edward H. Sheers, American Cyanamid Co., Linden, N. J., and Morton S. Cole, Sylvania Electric Products, Inc., Flushing,
T.Y. , As-Wagner-Pregl apparatus [Parnas, J. K., and Kagner, p r B i o c h e m . Ztg., 125, 253 (1931)l for the micro-Kjeldahl determination is undoubtedly the most widely used in the United Rtates. One of its drawbacks is the necessity for removing the flame a t the end of each distillation and waiting for the water in the stream generator to cool sufficiently to create the partial vacuum necessary to draw the spent sample into the steam trap for removal. I). 1,. Shepard and AI. 13. Jacobs have recently suggested the addition of a steam escape valve to the steam generator ‘ J . Am. Pharm. Assoc., 40, 154-5 (1951)]. This valve, which is closed during the distillation by means of a pinch clamp, is opened a t the end of the distillation and the pinch clamp is then placed between the steam generator and the steam trap. This modification considerably lessens the time and effort required to miry out a determination. The following modification cliiiiinate, completely the necessity
The addition of D allows the use of the spent condenser water to keep the outlet tube to the sink constantly clean. The apparatus as modified thus need rarely be disassembled in normal use. I n areas where the tap water contains titratable amounts of ammonia, it is suggested that the water inlet to the steam generator lie connected to a container of distilled water. Calculator for Selection of Sample Weights in Microdetermination of Carbon and Hydrogen. Ruth C. Thompson (present address, Kesleyan Universit,y, Middletown, Conn.), Laboratory of Advanced Research, Remington Rand, Inc., South Sorn.alk, Conn. niicroanal?-tical work the sample weight is Is r l r c t d :iccording to the percentage of the constituent to be determined ( 3 ) . If more than one constituent is t o be deterY QL-~STIT-~TIVE
mined, the srlcction becomes more complex. I n the microdetermination of cnrbon and hydrogen, for example, a sample weight which produces a suitahle amount of carbon dioxide for a carbon determination might produce so little mater that thr accuracy and precision of the hydrogen determination are impaired. 4 compromise saniplc size should be chosen which allows each element to be determined with the best accuracy possible. The precision and accuritcy of the hydrogen tktcrmination depend also on the maintt,nance of the lead dioside-watercarbon dioxide equilibrium (8). If sample sizes a w selected SO that approximately the same amount of water will be produced in succrssive analyses. this equilibrium will remain undisturbed (7). Some niicrocheniists recommend using saniples oi 4 to 5 mg. (61, 4 to 6 mg. ( d ) , or 10 to 15 mg. (j)thus , disregarding the aforenit,iitioiir.d con~idcrations, -4 v : i r r h of tht. 1iter:tture re-
