GB878197A - Torsion balance for the determination of small variations in the apparent weight of samples - Google Patents

Abstract

878,197. Weighing apparatus. MINISTERAL INDUSTRIEI PETROLULUI SI. CHIMIEI. March 18, 1959, No. 9474/59. Class 143 [Also in Group XXXVI] A torsion balance comprises a moving element provided with a horizontal torsion thread and a float which, when immersed in a liquid whose free surface is at the level of the torsion thread, supports the weight of the moving element. The balance is designed for the measurement of small changes in the effective weight of a load and is described with reference to the measurement of magnetic susceptibility of rock samples. The moving element comprises a pair of balance arms al, a2 connected by a ring b whose centre lies on the common axis of the arms. Suspended at the end of arm a1 is a scale pan which comprises a lower container 26 in which is placed a magnetic sample to be acted on by a magnetic field produced by coil 27, and an upper container 28 in which is placed sufficient non-magnetic ballast to make up the total load to a predetermined value which depends on the float volume and liquid density. The arm a2 carries a movable counterweight 7 and a concave mirror 8 which in conjunction with a scale 9 and lamp 10 indicates the orientation of the moving element. The float 12 is immersed in liquid in the container 18 and is attached to the moving element by means of the threaded rod 15, which may be hollow and whose position is adjustable within a threaded block 16 attached to a frame 11 carried by the ring b. A notched lever 30 which engages the frame 11 to hold it down by the tension in spring 34 provides a locking mechanism which is released by rotation of a cam 37. One end of the torsion thread 13 is attached as shown to the frame 11 at the level of the liquid surface and is colinear with a tensioning thread 14. The other end of the thread 13 is held by a torsion head 22 to which is attached a pointer 23, or a vernier, movable over a scale 24. Before use the balance is adjusted, with the said predetermined total load on the arm a1, so as to bring the centre of gravity of the loaded moving element into coincidence with the metacentre of the float, by suitable adjustment of the position of the counterweight 7 on arm a2, a weight 17 on rod 15, and the depth of the float below block 16. In use the same total load is contained in pans 26 and 28 together and the torsion head is rotated until a zero indication is obtained on scale 9. The subsequent small change in the apparent weight of the load produced by the energization of coil 27 disturbs the position of the moving element which is then returned to the zero position by rotation of the torsion head, the consequent change in the reading on scale 24 indicating the magnitude of the magnetically produced change in effective weight of the load.