Air Thermostat Research Articles

Air thermostat for high-resistance electrical standards

Air thermostat for high-resistance electrical standards

An improved and simplified design for a Hoeppler-type (rolling ball) microviscometer

A microviscometer of the Hoeppler (rolling ball) type requiring no more than 0.15 cm3 of fluid and allowing recognition of the type of rheological behaviour of nonNewtonian fluids of practical interest is described. Photodiodes are used as the detecting system for the transit time of the rolling ball, which is read directly on a digital electrical timer. Relative mean shear rates can be varied at will by changing the slope of the test tube. The temperature is controlled with an air thermostat (absolute accuracy +or-0.06 K). The viscosity range covered thus far extends from less than 0.5 cP up to the order of 10 P.

Calcification and decalcification rates in vitro. A new technique.

SummaryA sedimentation column apparatus was developed in which the rates of calcification and decalcification of bone and dentin could be followed readily and quantitatively. The method utilizes a long column with guiding channel and can be rotated inside an air thermostat. The rates of calcification and decalcification are measured by following the sedimentation velocities of the specimen in the column of calcifying or decalcifying solutions with time. The bone specimens used are very small. Typical results obtained in decalcification with EDTA and lactic acid, and of calcification rates of rachitic cartilage are presented and discussed.

The design of a general purpose air thermostat

The design of general purpose air thermostats is discussed and it is argued that the main problem is to control the distribution of temperature in space, control in the time dimension being relatively easy. It is shown how the amplitude of spatial temperature variations within the enclosure can be reduced by making the enclosure walls from a laminate consisting of alternate layers of conductor and insulator. The paper describes the construction of laminated wall enclosures and of the associated control system. Thermistors are used as the temperature sensing elements. Within such enclosures, the temperature has been held constant to within 10-4 degrees C at a point near the controlling thermistor and to within at least 10-3 degrees C over the remainder of the enclosure. The performance appears to be limited only by noise and drift in the thermistors.

Growth of Large Single Crystals. Ce2Mg3(NO3)12·24H2O (CMN)

An apparatus and method is described for the growth of large, flawless, high-purity, oriented, single crystal cylinders (at least 50 mm in diameter by 55 mm long) of cerous magnesium nitrate 24 hydrate [Ce2Mg3(NO3)12·24H2O; (CMN)]. The CMN single crystals are grown at 30 °C in an air thermostat by evaporation of a saturated aqueous solution using reagent H2SO4 (98 wt %) as a desiccant for H2O removal. Growth is in a cylindrical container with the c crystal axis oriented parallel to the cylinder axis. The container and crystal orientation limit growth in the fastest growing directions perpendicular to the c axis. Rate of growth parallel to the c axis is set at 0.9 mm/day. Large single crystals are assured provided the procedure described is followed rigorously. Fabrication of the CMN cylinders into spheres and the location and marking of the crystal axes are also described. A spark source mass spectrometer analysis of pieces of such CMN crystals gave an impurity level expressible as 615 < atomic ppm impurities <1710 (atomic ppm relative to Ce). It is suggested that the apparatus and method may find general use in the growth of large single crystals of other substances, perhaps with a modification to allow continuous solution addition.

Proportional thermoregulator using thyristors

A circuit employing thyristors and operational amplifiers can be used for proportional temperature control. The sensor is a thermistor. The thermoregulator will keep the temperature constant within 0.03 degC in an air thermostat with a heat loss of 100 W. The device is easily adapted to temperature programming.

Poly(1-Butene) Chain Flexibility from Sorption Data

Abstract A previous investigation of the sorption properties of polyethylene over a wide range of temperatures, above and below the melting point, showed that this polymer, the simplest member of the polyolefin series, has chains of quite high flexibility, a factor which also governs its extent of crystallization. The present work is devoted to the study of the sorption properties of crystalline polybutene to obtain data on chain flexibility. This polymer is of considerable interest, since it exhibits elastomeric properties as well as crystalline structure. A polybutene sample with an intrinsic viscosity of 1.14 (determined in decalin at 90°) was used in the study. Observation in a polarization microscope showed that the sample melted in the temperature range 94.3° to 104.8°. Isotherms for sorption of n-octane by polybutene at 50°–115° (Figure 1) were obtained by means of a spring balance placed in a high temperature air thermostat. As Figure 1 shows, sorption increases regularly with temperature up to a relative adsorbate vapor pressure of 0.45, with the exception of the isotherm obtained at 50°, which lies above the isotherm at 60°. This somewhat unexpected result is possibly associated with the less dense packing of the chains at 50°, a factor which also results in higher sorption. At higher relative vapor pressures, when chain flexibility increases as a result of the plasticizing effect of the solvent, the density of molecular packing increases, and sorption becomes lower than at 60°.

Adsorption on measured surfaces of vitreous silica—II

In earlier experiments (Part I Palmer 1935) a method of estimating the adsorption area of powdered silica was developed, and absolute measurements were obtained of the adsorption at 25° of a variety of volatile substances, but the relative pressure of the vapour phase was confined to a range below 0·5. An account is now given of similar measurements in which the pressure was taken to saturation with the typical substances benzene, acetone and methyl alcohol. Some modifications were made in the apparatus (shown in fig. 1 with lettering corresponding to Part I, fig. 1, p. 361) to cope with the larger adsorptions at higher pressures and the special difficulties in working with vapours near saturation. The superheating bulb C was immersed in water kept at 70-80° to ensure dryness in the vapour entering the storage bulbs B 1 and B 2 through the mercury trap a . The bulbs B 1 and B 2 were each of about 50 c. c. capacity and provided with capillary inlets k 1 and k 2 . The calibrated bulbs B 3 (total volume 40 c. c.) and the upper manometer point b 2 were added so that, by allowing mercury to flow from some or all of B 3 , pressure in the storage system could be lowered and read with b 2 without affecting the pressure in the adsorption tube A . This was especially necessary in experiments with methyl alcohol whose vapour shows very marked imperfection near saturation. A large air thermostat kept the whole apparatus at 25 ± 0·3°. As before, taps were completely excluded from the measuring parts of the apparatus.

Studies in Refractive Index Part IV*

In this paper an account is given of an extension of the second method for determining refractive indices of liquids in thin films, previously described in Part I of this series. The apparatus was modified mechanically and optically and an air thermostat built to contain it. The critical angle of reflection from glass to liquid was determined for three normal fatty acids, undecylic, lauric and myristic, in the molten state. The surface layers of the liquid phase were observed to become suddenly birefringent within a narrow range of temperature immediately above the temperature of solidification, thus indicating orientation of the molecules of the molten acid to a depth of at least a wave-length or so of visible light.

An accurate form of Huygen's manometer adapted as a tensimeter

An accurate form of Huygen's manometer is described, with special reference to its use as a tensimeter. Difficulties due to irregularities of the cross-section of the manometer tube, in the graduation of the scale, and in the glass of the air thermostat window, and to deviation of the manometer and the cathetometer from the vertical are avoided by direct calibration against saturated water-vapour pressures over ice or water. Effects due to warping of the wood frame and support after calibration are avoided by a levelling device. The sensitivity is 0.001 mm. Hg, and the accuracy is limited by the degree of precision with which the temperature of the water or ice can be maintained and measured with the standardized thermometers usually available.

An air thermostat for quantitative laboratory work. The quantitative humidification of air in laboratory experiments. Discussion

The first page of this article is displayed as the abstract.

An air thermostat for quantitative laboratory work

An air thermostat for quantitative laboratory work

A simple air thermostat

In this note a simple form of air thermostat is described, and a formula for the sensitivity is given.

On the Action of Insulin on Glucose.

An attempt was made to repeat the experiments of Lundsgaard and Holboll in producing a new form of glucose by the action of insulin upon glucose in the presence of live tissue. The glass apparatus used was entirely of pyrex glass. For the incubation, an air thermostat was carefully controlled at 37° C. Twenty-five grams of finely cut muscle tissue of guinea pigs or rabbits were used with 25 and 50 units of Squibb's insulin, and 2 grams of Pfanstiehl glucose in 100 cc. of 0.9% NaCl. In a few cases, 0.001 grams adrenalin were added. Proper precautions to maintain sterile conditions were observed. The dialyses were made through clear collodion membranes which were one to two mm. thick. The degree of rotation of the dialysate was determined with a Schmidt and Haensch polarimeter, using light which was filtered through solutions of potassium dichromate and vanadium sulphate. The chemical analyses were made both by the Hagadorn-Jensen method and the micro method of Benedict as modified by Peters. In no case was there a marked difference between the amounts of sugar determined by chemical and physical methods. What is more important, the degree of rotation of the dialysate was not found to have changed after these solutions had stood for 16 to 40 hours. The degree of rotation of the dialysate of samples of blood, presumably high in sugar content, was found to be too small and uncertain to deserve consideration.

AN AUTOMATIC DEVICE FOR TAKING MOTION PICTURES AT REGULAR TIME INTERVALS1

ABSTRACTAn automatic apparatus for taking single photographic exposures at regular intervals of time over periods of from 12 to 36 hours was constructed. It consists of a large air thermostat and three mechanical units: (1) the thermal regulator, (2) the illuminating and optical system, and (3) the automatic mechanism controlling the camera and illuminating system. A detailed description of the construction and operation of the apparatus is given.