A systematic handbook of volumetric analysis, or, The quantitative estimation of chemical substances by measure, applied to liquids, solids and gases / by Francis Sutton.

  • Sutton, Francis, 1831-1917.
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: A systematic handbook of volumetric analysis, or, The quantitative estimation of chemical substances by measure, applied to liquids, solids and gases / by Francis Sutton. Source: Wellcome Collection.

    32/592 (page 16)
    S 8. ON THE CORRECT READING- OF GRADUATED INSTRUMENTS. § 8. The surface of liquids contained in narrow tubes is always curved, in consequence of the capillary attraction exerted by the sides of the tube, and consequently there is a difficulty in obtaining a distinct level in the fluid to be measured. If, how- ever, the lowest point of the curve is made to coincide with the graduation mark, a correct proportional read- ing is always obtained, hence this method of reading is the most satisfactory (see fig. 16). The eye may be assisted materially in reading the divisions on a graduated tube by using a small card, the lower half of which is blackened, the upper re- Pig. 16. maining white. If the line of division between the black and white be held about an eighth of an inch below the surface of the liquid, and the eye brought on a level with it, the meniscus then can be seen by transmitted light, bounded below by a sharply defined black line. A card of this kind, sliding up and down a support, is of great use in verifying the graduation of the burettes or pipettes with a cathetometer. Another good method I is to use a piece of mirror, upon which are gummed two strips of black paper, half an inch apart; apply it in contact with the burette so that the eye can be reflected in the open space. The burette or pipette is filled with water at the proper temperature, and the contents of each division of 10 c.c. or so carefully read off with the telescope and weighed. In order to do this with pipettes they must be fixed in a burette support, and have over their upper end a tightly fitting elastic tube closed with a pinch-cock. The operator may here consult with advantage the details of gradu- ating and verifying measuring instruments for the analysis of gases as described in Part 7. In taking the readings of burettes, pipettes, and flasks, the graduation mark should coincide as nearly as possible with the level of the operator’s eye. Erdmann’s Float. This useful little instrument to accompany Mohr’s burette, gives the most accurate reading that can be obtained; one of its forms is shown in fig. 17, another, containing a thermometer, is shown in fig. 4. It consists of an elongated Pig. 17.