Details
An extremely fine and extremely rare gilded precision analytical balance, the "Vacua", by Sartorius AG,
circa 1952, with glass dome -- 25¾in. (65.4cm.) high
The Vacua was marketed by Sartorius AG from the early 1950s. It was available with numerous special fittings, accessories and modifications, in order to allow its application to many different experiments and tests. This spectacular example enabled the user to weigh in a vacuum, to do hydrostatic weighing or to do the earliest type of thermo-gravimetric analysis (TGA). Because it might be used in a corrosive environment, it was thickly protected with gold-plating. The following description assumes that the front is the side from which the readings are taken, so the beam is mounted behind the pillar. The weight-loading is operated from the right-hand side. The measuring of the rate of chemical reactions (TGA) was done from the left-hand side.
The beam is a traditional Sartorius design, with four circular cut-outs, and sensitivity-adjustments in the end holes. It has three agate knives that are ground to 60°, bearing on planes in brass compensation hangers. The compensation hangers have cone-and-cup bearings, with the cones bearing on ruby cups.
Because the balance is a vacuum balance, air- and oil-damping are not practical, so magnetic-damping is used. A vertically-mounted vane of aluminium rises up from the beam to pass between two magnets, for eddy-current damping.
From the rear of the beam a 100mm-long descending arm has a graticule mounted at its end. Via mirrors the reading is taken from the front of the balance. A light was mounted on the outside of the dome, attached to the brass base, to illuminate the graticule.
The pans, of 80mm diameter, are typically-Sartorius design with deep rims sloping out and down, with pans and support wires made of brass. The pillar, about 275mm high, is mounted on a black glass sub-base, 190 x 150 x 16mm, supported on four stout brass legs 50mm high, with a threaded peg joining the leg to the base. The base contains a push-rod for arresting the beam. The arrestment is the two-centre radial system.
The pillar has sub-assemblies mounted on it, including the lens and mirror for optical projection, and the optical projection screen and mirror mounted on front foot of the pillar, mentioned above. An electric motor (12/24 V 50C AC) with electrical terminal block of 10 for separate mains input, drives the TGA mechanism, which is mounted (when needed) beside the motor. The motor drives the loose suspended assembly, (which takes the place of the load pan). Also attached to the pillar is a mirror tilting to view down the hole under the load pan (which is removed when TGA or hydrostatic work is undertaken). Lastly, a plumb-bob is attached to the pillar.
The most-eye-catching section is the weight-loading mechanism. The banks of weights are supported on arms coming out of a rectangular box, which has, at its front corner, the shaft that lowers the weights, and at its rear, the shaft that turns the mirror-finish discs with pins that connect sequentially with cams. The cams push down levers that, at their other ends, connect with the shaft that lowers the weights.
The top of the box supports a curved graduated arc that indicates, by the pointer passing over its surface, which of the weight-banks has been activated, i.e., the weighing range. The fully-automatic, externally-driven weight-loading system has four banks of weights, reading to four places. (Capacity 99.99grams + 2 places optically).
Bottom bank 10-90g. (10 10 50 10 10)
Next up 1-9g (1 2 5 1)
Next up 100-900mg. (100 200 500 100)
Top bank 10-90mg. (10 20 50 10)
Graticule 0-9mg, reading presumably to 5 places, but not tested because no electricity was applied.
All the banks work off one shaft via bevelled gears with automatic coupling. This enables the selection of weight-bank and sequential loading with one hand-wheel, and the second hand-wheel operates the beam release. The two hand-wheels operate the electro-magnetic weight-loading only. The top-surface of the base has two guide-blocks angled out towards the front, very carefully attached, but their function is not known.
The TGA mechanism is called "Measurement of the rate of chemical reactions, which run under weights-alteration, at any temperatures, using a high frequency furnace" in the 1952 catalogue. This is of particular interest to historians of chemistry because the special attachments with the Vacua show the earliest attempts to provide this facility to test hydrates, plastics and synthetics. The surface-tension mechanism was not in the catalogue, and all the bits for it were attached by additional brackets, as if this was a special, individual order, needed by the one client, and not required by most customers. It adds even more interest to this rare balance, and causes one to ponder the original client's needs. The mechanism could only be used when the load-pan and its hanger was removed, and a simple hanger hung in its place. Then the rotating arm and its reel of wire was hung below the hanger, interlinking with the little motor mounted on the pillar. When the motor was switched on, the arm revolved, the wire wound up, and the sample mounted on its lower end was pulled up through the furnace. The sample was viewed through the angled mirror mounted on the pillar. When the bob had risen sufficiently, the motor was switched off and weights were applied in the normal manner, until the bob was freed from the surface. Obviously, when this mechanism was being used, the dome was not covering the balance, so no vacuum was being applied and it did not matter that the hole in the base was open. (If the balance was being used as a vacuum balance the holes in the base were carefully plugged by caps below the base).
The whole balance is on three legs, that must have been carefully arranged, originally, over a large space, to give good access, and to permit the use of containers below for TGA work and for hydrostatic weighing. Given the weight of the glass dome and the delicacy of the balance, this structure must have been very carefully engineered.
Order of weighing:
1 Plug in electricity.
2 Make sure the arrestment is locked.
3 Load.
4 Release the beam by rotating the beam by releasing the front hand-wheel somewhat.
5 Rotate the rear weight-loading handle (further from the operator) that will drive the coarsest bank of weights (tens of grams) to bring the weights near to, but less than, the load.
6 Continue to rotate the black release handle (further from the operator) until the second bank of weights is selected. This enables the second bank of weights (single grams) to bring the weights near to, but less than, the load.
7 Repeat the turning of the black release handle to select the next bank. Load weights as required always keeping the pointer at the top of the box within its range.
8 Repeat until top bank is reached.
9 Check graticule to see if the balance is balanced. If so, allow it to come to rest and read off.
With thanks to Ritzo Holtman for his help in finding Sartorius-Werke catalogues, and for his translations. Thanks also go to the curator of the Sartorius Museum, Dipl. Ing. J Barankewitz, for his assistance.
Compiled by Dr T. Allgeier, Dr P. Buchanan, D. Crawforth-Hitchins & B. J. Oliver
See Front Cover Illustration, Colour Illustrations and Detail
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