Adjustable Voltage Thermostat System W. C. GRIFFIN Central Research bboratoty, Atlas Powder Company, Wilmington,
A
750-, and 2000-watt sizes-200B, 2OOCU and CM, and lOOQ, respectively, made by the General %$io Corp., Cambridge, Mass.-have been employed for these circuits. They have auxiliary taps 2 and 5 illustrated in Figure 1.) Approximate volbges supplied, with the transformer wired to supply 0 to 135 volts, are indicated in Figure 2. The circuit is not useful a t a setting of less than 15 volts, because of reversal of voltage, as shown in Figure 2. Low voltages are seldom used; for lighter heat loads, lower wattage heaters are usually used and these require a correspondingly higher setting. If the singlepole double-throw switch were mounted between points 1 and 2 on the input side of the autotransformer. the low voltage would always he approximately 80% of the high voltage. Unfortunately, the switch must then break a very high inductive load and the benefit obtained would not warrant the added cost of the high-capacity switch, I n the present assembly, a micraswitch (15-ampere capacity) suffices to carry the output load
UTOMATIC temperature control is desirable for many laboratory reactions. Thermostats of suitable sensitivity are available, but they usually must he built in the equipment and often utilize several heaters. The assembly described was devised to he used with any one of several standard laboratory electric beaters, to be flexible in the choice of temperature, eompact, and low in cost. With any standrtrd single element heater i t gives the effect of having a large k e d heater with a m a l l amiliary control heater. It waa quickly found that reguhr laboratory heaters used in conjunction with "on-off" thermostats give poor control, be cause the heater is either completely on or completely off. The circuit in Figure 1 was devised to supply a portion of the heater voltage continuously with an increased voltage upon demand of the thermostat. A laboratory autotransformer is combined with a thermostat operating a singlepole double-throw switch. (Variacs of ZOO-,
Figure 2.
Voltaee
VI.
Dial Seiting at High and Requirements
Del.
Figure 3.
Low Thermostat
Portable Unit
Combines G n . d Radio Type PW CM V a d s d l h silo1 lisht B
671
672
INDUSTRIAL A N D ENGINEERING CHEMISTRY
(Microswitch thermostat used waa a Type T-2-b Ther-Mu-Trol, Mu Switch Co., Canton, Maas.) Pilot lights indicated in Figure 1are 24- or 30-volt bulbs. O g eration of the lights is opposite that of the switch-i.e., the light across pole A lights when the switch is in contact with pole B. Thus the thermostat is on “high” heat when pilot light B is illuminated. The addition or substitution of a 24volt bell or buzzer for pilot light A,with the inclusion of a controlling switch, provides an audible signal that has been found most useful. It permits safe initial heating of a reaction a t a voltage higher than that needed to maintain the reaction temperature. .When this thermostat setting is attained, the buzzer sounds until the switch
Vol. 17, No. 10
is opened. This signal indicates that the Variac setting should be reduced to the proper operating voltage. Choice of the thermostat depends upon the requirements of temperature control, available space, permissible size of sensitive elements, corrosion problems, etc. The one requirement for this assembly is that it operate a single-pole double-throw switch. Succeasful operation has been obtained with several types of thermostats. The apparatus has been used to heat reactions in flasks, beakers, etc. Control at temperatures of 200’ to 300’ C. is within *2O C. The principle is applicable to constant-temperature baths, ovens, and other electrically heated laboratory apparatua.
Device for Vacuum Sampling of Liquids and Suspensions W. J. McBRlDE AND L. N. PRESTON Fullers’ Earth Union, Ltd., Redhill, Surrey, England
W
HEN sampling liquids and suspensions contained in large tanks, tubes may be inserted a t various levels through the tank side or a plunger-operated device may be dipped into the liquid to any desired depth. These methods both present objectionable features in that it is not possible to take many simultaneous samples almost instantaneously. The authors have developed a method based on that used by McBride in Australia in 1900-1920 for the simultaneous sampling of mine gases a t many points and have improved it and applied it to taking as many as a dozen 1-liter samples in sedimentation tanks up to 600 cm. (20 feet) deep in which are revolving thickener paddles, and also to taking samples in viscous suspensions of 1.25 specific gravity. The method involves the almost simultaneous opening of highly evacuated bottles a t suitable sampling points by withdrawing stoppers from them. This avoids the use of taps and makes possible continued operation of the device in abrasive suspensions in which taps could not be expected to remain vacuum-tight. The conditions of operation preclude the use of anything other than a very easily portable apparatus, and since I-liter sample8 we necessary for the authors’ application, the whole device is strongly made. The apparatus is of very simple construction, each liter bottle being fitted with a rubber stopper carrying a tube of about 1-cm. bore and 10 cm. long, This has a 6-mm. bore side tube fitted with a piece of rubber pressure tubing closed by a screw clip. The outer end of the wide tube is closed by a greased glass stopper ground to fit inside it. The whole bottle is held in a wooden cradle by a strong rubber band and as many bottles as may be necessary are clamped by screws or fingernuts and bolts to a ‘/,-inch iron pipe which may be 25 feet long; if long, it is jointed for ease of assembly. The bottle stoppers are connected one to another by cords which ullow a few inches’ slack. I n use the bottles are evacuated via the side tube, put each in its appropriate cradle, and the stoppers are connected together. The rod carrying the bottles id introduced to the desired depth into the tank of liquid to be sampled and the stoppers are pulled out by their connected strings. This can be done with only a 1-second interval between the removal of one stopper and the next, and the force necessary to remove each stopper is a good guide to the vacuum in each bottle. Since the bottles fill completely, there is no subsequent contamination of their contents HS they are raised to the surface. The apparatus as described is in use for the weekly investigation of sedimentation rates in tanks ranging from 14 to 20 feet in depth, while a shorter form carrying three bottles is used in tanks
about 6 feet deep in which a variety of viscous suspensions up to specific gravity 1.25 is settled. Various refinements of construction and alteration in the m terials from which the device is made should make it applicable to other purposes, In particular, the size could be greatly reduced. ACKNOWLEDGMENT
The authors are indebted to the Fullers’ Earth Union. Ltd.. Redhill, Surrey, England, for permission to publish this note.
A
Safe Device for Distillation in the Kjeldahl M e t h o d
MARIO M E N E G H I N I , Instituto-Biologico, SZo Paulo, Brazil
I
N RESEARCH work with the Parnas-Wagner micro-Kjel-
dah1 apparatus for nitrogen microdetermination in citrus stems, it was frequently necessary to use larger quantities of reagents than usually are employed. This fact increases the risk of the standard acid’s 5owing through the condenser tube into the distilling 5ask. This happens principally at the moment when the concentrated sodium hydroxide is added at the, beginning of the distillation. According to the author’s experience, the simple addition of a Bunsen valve to the receiving flask efficiently prevents apoiling the analysis. The diagram shows how to adapt the valve to the apparatus. The receiver, a , is fitted with a rubber stopper, b, furnished with two holes, through which pass the lower end of the condenser tube, E , and the tube of the valve, d . After the first part of the distillation is finished, the receiver is removed, leaving the rubber stopper with its valveattachedto thecondensertube.
