Pikaõlalised analüütilised kaalud Tartu Ülikooli muuseumis
Creators: name: Ilomets, Tullio
Publisher: name: Tartu Ülikooli ajaloo küsimusi
Year: 2014

description: Long-beam Precision Balances at the University of Tartu Museum Tullio Ilomets University of Tartu Museum There are a number of historical long-beam precision balances in the University of Tartu Museum collection, most probably dating back to the first half of the 19th century; this article introduces two of those balances more closely. According to oral tradition, the first of the balances belonged to Carl Ernst Heinrich Apollon Schmidt (1822–1894), a professor of chemistry at the University of Tartu in 1847–1892, and the balance was preserved in the department of chemistry chair of inorganic chemistry. The balance was handed over to the museum in 1982. The second large analytical balance, a so-called one-kilogram scale was made in the workshop of the famous Berlin balance craftsman Johann August Daniel Oertling (1803–1866). The balance bears the inscription: Aug. Oertling in Berlin № 1329. The balance was handed over to the museum by the chair of inorganic chemistry on 11 June 1993. The balance of Carl Schmidt can be disassembled into five parts that are packed into the drawers of a mahogany balance case, each part to its proper place. The balance is made of light brass. The measurements of the balance case are 51.5 x 13.5 x 8.5 cm. The drawer of the case can be locked. On top of the case, there is a brass plate with the measurements 3.0 x 3.0 x 0.6 cm in the centre of which there is a threaded opening, where the column is connected. The front edge and edges of the balance case have metal feet the height of which can be adjusted. The main part of the column supporting the balance beam is a 1.9 cm-in-diameter solid brass cylinder, while the eccentric and scales are situated just below it. There is a console attached to the top part of the column; on top of that, there are two round agate plates, which support the knife edge of the beam’s prism. The full length of the column is 28.5 cm. The moving part of the column consists of two cylinders that are connected with three rods, are positioned around the column and can be moved up and down. A frame with two notches surrounding the console and a forked arrestment device for the beam positioned perpendicularly with the frame are attached to the upper cylinder. The lower edge of the lower cylinder touches the eccentric. If one rotates the eccentric, the frame moves up and positions itself in the notches above the prisms’ ends, the forked arrestment device fixes both sides of the beam in the grooves at the ends of the forks. This system of arresting the balance beam was first used by August Oertling. The arresting system of Carl Schmidt’s balance is very similar to an Oertling-type balance described in older literature. This except for the fact that in case of Oerlting’s balance, the arrestment system of the balance is lifted by the eccentric with the aid of a rod within the column. Carl Schmidt’s precision balance has a rhombic structural beam with two vertical crossbars. The beam is graduated on one side for the manual positioning of the rider. The length of the beam is 42 cm. In the middle of the beam on its upper edge there is a device that allows regulating the centre of gravity of the beam; on the lower edge there is a downward pointed needle. On both ends of the balance beam there are the so-called swan necks that are bent upwards into curves and have two regulating screws; their lower ends are circle-shaped and the suspension threads of the balance bowls are attached to these. Oertling’s balance also has these swan necks. The balance has no notations regarding its manufacturer, as well as the time and place it was made. Neither does it have a university inventory number. We may presume that the balance is an earlier version of an Oertling-type balance and it belonged to Carl Schmidt personally. Judging by construction, the balance was made in the first half of the 19th century. Oertling’s large analytical precision balance is made of brass and preserved in a mahogany case, which has glazed doors on the sides and glazed wooden frames that can be lifted to the required height on the front and back sides. There are two brass feet with adjustable height under the balance at the corners on the front side and a single brass foot in the centre of the back side. The balance case can be locked. There are dampers that hinder the oscillation of the balance bowls in the bottom of the balance case. Front centre, there is a round fluid level for levelling the balance. Under the balance bowls, there is a round hole in the bottom of the balance case, and it has a brass cover that can be slid aside. A device for mounting the reiter balance beam is attached to the ceiling and right-hand inner wall of the case. The measurements of the balance case are 80.0 x 54.0 x 24.0 cm. The height of the lower part of the case is 6.0 cm. The balance column is attached to a brass plate measuring 16.0 x 8.3 x 0.7 cm at the bottom of the case. At the point where the lifting mechanism side forks come out of the column, the diameter of the column is 4.0 cm, upwards, it is 3.0 cm. The total length of the column is 27.7 cm. A plate measuring 4.0 cm x 4.0 cm x 0.9 cm has been attached on top of the upper plate of the column; on top of that, there are two parallel-positioned 5.8 cm high bearers that are 1.2 cm apart – these are meant for supporting the round agate plates. A scales mounting frame with a rhombic structure attached with six vertical crossbars is attached to the back of the column; its length together with the scales is 61.5 cm. The moving part of the balance column is made up of the beam’s arresting frame that is 67.0 cm long and consists of two halves 2.8 cm apart from each other. Both sides of the frame have a rhombic structure as well and they have six vertical crossbars. The central part of the frame, which is 5.4 cm high, is attached to the plate at the bottom on both sides; the plate features holes that fit the agate plate bearers exactly. The plate is connected to the tip of the rod that moves up and down inside the column. A triangular notch is aligned with the prism at the extension of the upper side of the frame’s central part. The two sides of the arrestment frame have been connected with cross strips, while external rods that are 30.0 cm long, reach out from the openings in the lower part of the column, and are connected to the rod inside the column, are attached to the strips. On the ends of the arrestment frame, there are triangular notches above the balance beam’s end prisms on the upper edge. Upon arrestment, the frame lifts the middle prism of the beam from the agate plates into the notches. At the ends of the beam, the frame lifts the forked suspension frame of the balance bowl together with the agate plates from the prisms into the notches. The upwards and downwards movement amplitude of the frame is 1.0 cm. The balance can be arrested with a disc on top of the balance case, which is connected to a lifting mechanism inside the column via the axis. Oertling’s large scale has a rhombic beam with six vertical crossbars; its length is 55.0 cm, its width at the point of the supporting prism is 5.0 cm and thickness 0.9 cm. In the centre of the beam on its upper edge above the supporting prism there is a device for regulating the centre of gravity of the balance beam. The beam has no pointer. The ends of the beam are forked. The upper forks have points that reach the scales. The beam is balanced when the points are on 0 noted on the scales. The lower forks of the beam ends have prisms that carry the balance bowls. The front part of the beam’s upper edge on both sides of the prism is graduated. There are two graduations: upper and lower. The lower starts from the middle prism and runs to 10. The upper graduation starts from the middle of one side of the beam with 0 and runs to 10 on both sides of the 0, while each of the units is divided into five parts in their turn. The diameter of a balance bowl is 10.0 cm. Under the balance bowl in the middle, there is a loop, which can be used to attach a fine wire or a hook and thread that come from the opening under the balance bowl. This allows to use the balance as a hydrostatic balance. As there are no points of comparison, the time when August Oertling’s long-beam precision balance No 1329 was made is unclear for the time being. If we are to presume that the balance was made during Oertling’s lifetime, it could be dated to the first half of the 19th century; the number most probably denotes the serial number of the manufactured devices. The article provides a short overview of the history of long-beam precision scales, mainly on the basis of the researches of Hans R. Jenemann on this subject. Jenemann defines the age of the long-beam precision balances with the years 1775–1875. The article also briefly discusses the achievements of the preceding age in perfecting assay balances. The author also introduces the basics of balance theory in connection to the possibilities of increasing the sensitivity of balances.
description: Tartu Ülikooli ajaloo küsimusi, No 42 (2014): Ülikool ja keelevahetus