Switching System for Beckman Absorption-Flame Spectrophotometer. .;i. L. Dunn, F. L. Humoller, and A. R . McIntyre, Depariinent of Physiology and Pharmacology, University of Sebraska College of Medicine, Omaha, S e b .
tube compartment was maintained by the use of soft-rubber gaskets under the steatite pillars and a soft-rubber grommet around the knob shaft. Electrically the switch assembly carrying the two resistors is substituted for R16 in the circuit diagram of the Model DU spectrophotometer.
.tudies of l~iocheinicalchanges in muscle following 1."neurotomy and tenotomy carried out in this laborat'ory during
A Beckman rpectrophotometer-flame photometer modified as described has been in constant use for over two years. The stability of the instrument is unimpaired in any way. Recently Sational Technical Lahoratories have met the need for such a switching device 11 ith a i esistor slyitching hou which is supplied nith current inqtruinents and which may be attached t o the older models if desired The authors' version provides an rntirely satisfactory svsteni at a very modest cost foi thow who may wish to undertake the niodification themselves.
tlie p3.d two years [Humoller, F. L., Griswold, R., and McInt'yre, A . R,, J. Gen. Physiol., 33, 723 (195O)l extensive use n-as made of the Rcckman Model DU photoelectric quartz spectrophotometer with the flame photometer attachment. Those familiar with the earlier model of the Beckman instrument are axare that the resistor changes necessary to convert it for use with the flame photometer at,t,achment and back again for use in absorption spect,rophotonietryare time-consuming anti require considerable skill and c ~ n r ~ .
Improved Pycnometer for Powders, Precipitates, and Synthetic Resins. V. F. Downing (present address, Lederle Lahoratories Division, .inierican Cyariamid Co., Pearl River, N. Y.), and F. R . Parker, Chemical Department, American Brake Shoe Co., lIah\vah. S.,J, spwial types of glass pycnornet,ecs have been denilvised as aids in obtaining the specific gravity and density powdered vkcous niaterials ( f - 4 ) . Although most, of these 4
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are admirably adapted to the problems for which they have been devised, there seems t o he a need, especially among workers engaged in plastics I t i ~ h for , a pycnometer which overcomes the fulloffing difficulties:
Figure 1. Constructional Details of Switch
In order to eliminate this exchanging of rrsistors, the authors modified their inst,runient in such a manner that the 2000megohm resist,or, for absorption Ppectrophot,onietry, or the 10,000-megohm resistor, for flame photomet'r>-,could be connected into the circuit instantaneously n-ithout opening the photot.ube compartment. I n Figure 1 is s h o m the switch used in the modificat,ion.
The narrow necks of moit, pycnometers make thein difficult to load with pori-dered or viscous materials and difficult to clean after use. The lack of an attached thermometer as an integral part of pycnometers specifically designed to handle viscous materials makes temperature control somewhat uncertain-a material will eventually come to equilibrium in a constant-temperature water bath, but just when a given material first attains such an equilibrium has frequently been difficult to determine. hfultiple determinations necessitate the purchase of a number of expensive units or, alt,ernatively, the consumption of a large number of man-hours xhen using a single pycnometer and its t ared dupiic ate.
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Only part,s obtainable a t a radio supply store were used. As availaide space in the phototube compartment is limited, the pillars on n-hich the switch contacts and the switch blades are mounted can be no higher than about 0.75 inch, although it would be desirable to have t,he leakage paths longer. The authors employed steatite insulation in their instrument, but polystyrene or material of similar insulating qualities would serve as well. The s\r-it,ch blade and silver contacts were obtainable by dismantling a heavy-duty telephone jack. The clips which hold the resistors on the steatite pillars were taken from mountings for small tubular fuses (Type 3AG or 4AG). The insulating pillar carrying the movable switch blade was mounted on a Centralab K-121 indexing assembly, whose shaft projects through the roof of tBhephototube case and carries the pointer knob. This indexing assembly assures positive positioning of the switch blade on one or the ot,her contact. The switch is a single-pole double-throw type; one of the stationary contacts is hidden because of the perspective of the drawing. I n the authors' instrument the assembly shown in Figure 1 is inverted and mounted on the roof of the phototube compartment. A pointer knob outside the case operates t,he switch. Approximate dimensions are given, but they may be varied to suit the available materials. The extreme importance of good insulation must be kept in mind, lest the stability and accuracy of the instrument be impaired. Hermetical sealing of the photo-
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The design of the pycnometer presented here seems to be the answer to the above problems, even though the difficulties encountered in the determination of the density of any given 229
