A modification of the deflection balance for use in biochemical laboratories / by John William Trevan.

  • Trevan, J. W. (John William)
Date:
[1926?]
Catalogue details

Licence: In copyright

Credit: A modification of the deflection balance for use in biochemical laboratories / by John William Trevan. Source: Wellcome Collection.

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    R [From THE BIOCHEMICAL JOURNAL, Vol, XX, No. 2, 1926] [All Rights reserved'] PRINTED IN GREAT BRITAIN !%. \ A MODIFICATION OF THE DEFLECTION BALANCE FOR USE IN BIOCHEMICAL LABORATORIES. By JOHN WILLIAM TBEVAN. From the Wellco?ne Physiological Research Laboratories, Beckenham, Kent. (Received March 11th, 1926.) The instrument to be described was evolved for the purpose of weighing out small quantities of reagents of the order of 10 mg. more rapidly than is possible on an ordinary chemical balance. It has proved very easy to use and may find other uses. It can replace the torsion balance of any range and costs approxi¬ mately £2. 10s. 0d. to make. Similar deflection balances have been used before [Salvioli, 1919; Research staff of G.E.C., 1923]. Salvioli used glass fibres, which are too fragile for common use, and observed the deflection with a microscope. The G.E.C. instrument has a steel wire but no scale pan and the deflection is observed by projection. The microscope (or projection system) has been replaced in the instrument to be described by a simple magnifying glass and the glass fibre by a steel wire which can be quite roughly handled without altering its calibration value. The base of the balance consists of a wooden block A mounted on tripod screws P. Fastened to the top of this is a brass plate L, which, to ensure rigidity, is attached by eight screws. On top of this at one end is attached the brass or wooden block J, and fastened to the top of this is a brass or steel block K' with a longitudinal V-shaped groove in its upper surface. K is another similar block, with a groove on its lower surface, which is held on by the knurled nuts M. A small brass rod R is held between K and K', and to the end of this rod is soldered a tinned steel wire B, 0-039 mm. in diameter. The other end of this wire is bent downwards as in the figure and is rounded off on a hone. The deflection of this wire is used as the index of the weight of material placed in the scale pan E, the position of which is fixed in. relation to the wire by bending the wire B into the hook shown in the figure. The scale pan (see Fig. 1 d) is made of a thin piece of mica F, square in shape, to which is attached, by means of Chatterton compound, the fine (40 gauge) copper wire G bent into a hook which rests on the hook on the wire B. The weight of the pan is about 18 mg. On one occasion, a very dry frosty day, the pan and the slip of mica carrying the powder to be weighed were found to become electrified, by friction, and to be difficult, for that reason, to manipulate. This difficulty was overcome by gently breathing on the mica in