Ajalooline proovikaal Tartu Ülikooli ajaloo muuseumis

Abstract

An Assaying Balance from the First Half
of the 19th Century at the University of
Tartu History Museum

The University of Tartu History Museum’s collection of older analytical balances also includes an assaying balance probably from the first half of the 19th century. The balance belonged to the Tartu State University department of inorganic chemistry and was handed over to the history
museum in 1982, where it was first displayed in the same year during the exhibition of science history commemorating the 350th anniversary of the University of Tartu. According to the lore of the department the assaying balance had once belonged to Carl Ernst Heinrich Schmidt (1822–1894), who was once a chemistry professor at the University of
Tartu and had worked for the University in 1847–1892.
The balance is placed inside a birch wood box finished with red lacquer and with the measurements of 14.0 x 24.5 x 2.7 cm. The balance is complete and in working order. Six of the lighter weights are missing from the set of milligram weights that should consist of 16 pieces by regulation. The largest weight is 1,000 milligrams, the smallest was 0.1 mg. Two small separate and gilded balance pans have also
survived. The balance is assembled on top of the box of the balance. The balance beam is 17.8 cm long, the pointer of the balance is 8.0 cm long. The steel knife-edge bearing of the balance beam is supported by the steel bearing seat.
The pointer of the balance faces upward and reaches the dioptric needle. The back of the vane is covered with milk glass. The balance beam is made of brass, the pointer of steel. The diameter of the balance pans is 3.3 cm and depth 0.3 cm. The balance pans are suspended from three silk threads. The length of the silk thread from the balance
pan to the fastening hook is 11.0 cm. The balance is suspended from a lifting mechanism that enables to lift the balance up for the time of weighing. The  balance may be lifted and lowered with the aid of a string; one end of it is attached to the coil fastened to the top of the balance box from whence the string runs through two sheaves, while
the other end is fastened to the lifting mechanism holding the balance. The balance is equipped with a damper that reduces vibration.
The balance has been measured in detail so that it would be possible to compare it with other similar balances elsewhere.
The forerunner of this balance type is W. F. Lingke, master at the Freiberg Mining Institute’s portable assaying balance made in 1827 (Harkort’s scale). The balance belongs to Harkort’s blowpipe kit along with other items necessary for analyses. A balance made somewhat later by the same master which is nearly identical but equipped with a
balance damper is called Plattner’s scale and it is placed in a separate balance box. Both balances have a pointer and a vane with a needle facing upwards. The description and drawing of a scale with a balance damper were published in the first volume of K. F. Plattner’s monograph published in 1835 (Die Probierkunst mit dem Lötrohre). The third and
complemented issue of Plattner’s monograph (1853) includes a drawing of a balance made by the same master, which shows that a significant change has been made to the construction of the balance: the scale pointer and vane with the needle are facing downwards. Balances made later by the same company (see Burchard, The History and Apparatus
of Blowpipe Analysis) have downward-facing scale pointer and the needle of the vane is replaced with a scale with divisions. Proceeding from the changes in the construction of balances we may presume that our assaying balance, the pointer of which faces upwards and which has a vane, could have been made before 1853. The dimensions of our balance and Plattner’s scale practically coincide. This article provides an overview of the developmental history of assaying balances, using a selection of contemporary overviews on that subject as well as available and more important original sources pertaining to assaying balances for that purpose.
The drawings, descriptions and other information on scales are based on Georgius Agricola’s De re metallica libri XII (seventh volume of the 1974 German publication); Lazarus Ercker’s Der grosse Probierbuch von 1580 and Johann Andrea Cramer’s Anfangsgründe der Probierkunst published in 1746 and 1794. The article also offers a brief discussion on the golden laboratory, Das Goldhaus, of August the Kurfürst
of Saxony in his castle in Dresden, as well as the ruler’s activities in the field of alchemy, assaying, coinage; and a summary of the manuscript Churfürst Augusti Kunstbuch at the University of Tartu Library.