The practice of pharmacy : a treatise on the modes of making and dispensing officinal, unofficinal, and extemporaneous preparations, with descriptions of their properties, uses, and doses intended as a hand-book for pharmacists and physicians and a text-book for students / by Joseph P. Remington.

  • Remington, Joseph P. (Joseph Price), 1847-1918.
Date:
1885
Catalogue details

Licence: Public Domain Mark

Credit: The practice of pharmacy : a treatise on the modes of making and dispensing officinal, unofficinal, and extemporaneous preparations, with descriptions of their properties, uses, and doses intended as a hand-book for pharmacists and physicians and a text-book for students / by Joseph P. Remington. Source: Wellcome Collection.

    79/1092 (page 73)
    into twenty parts, and every other division numbered, from 0 to 10. A series of nine weights are furnished with the instrument, numbered from 10 to 90; these are to be added to the weight at the bottom to cause the hydrometer to sink, so that a reading may be had on the graduated scale; this reading added to the number on the weight em- ployed, gives a figure which indicates the strength of the spirit by referring to a table which accompanies the instrument. Joneses hydrometer is similar to Sikes's, but by many is regarded as an improvement on it. Dica^s hjfdrometer belongs to the same class. TwaddeWs hydrometer is frequently employed in England, and tech- nical works often quote the degrees of this scale. It is used for liquids heavier than water, and is graduated so that the number of the degree, multiplied by 5 and added to 1000, gives the specific gravity: thus, 20° Twaddell indicates the specific gravity of 1100 or 1.100; 50° Twaddell, 1250 or 1.250. BecFs hydrometer is rarely used or referred to : in this scale 0 corre- sponds to the specific gravity 1.00, and 30 to that of 0.850; the scale is extended equally above and below 0. For tables, see Bayley's Chemist's Pocket-Book, p. 178. ZanetlVs hydi^ometers have a scale which requires the addition of a cipher to the number of the degree to show the specific gravity. 2. Hydrometers in which the depth of immersion is constant, but the weight subject to change. FahrenheWs hydrometer was one of the first instruments of this class to come into general use. Robert Boyle described, however, in 1675, his New Essay Instrument,'' and Fahrenheit's hydrometer was very similar to it in principle; it had but a single mark on the stem, which was surmounted by a small scale-pan; weights were placed in the pan to cause the hydrometer to sink to the mark. Now, as this mark indicated the point at which the instrument would float in water at a given temperature when certain weights were placed on the pan, it follows that when it was immersed in a liquid of different specific gravity the weights would have to be changed to float the instrument to the fixed mark; the ratio which this weight bore to the weight used for water gave the specific gravity. Nicholson's hydrometer is similar in principle to Fahrenheit's, but is modified so that it can be used for taking the specific gravity of heavy or light solids. Fig. 48 is an illustration of one of the most convenient forms of the instrument; it (^'^^ is usually made of brass; there is a single mark V^^^^ on the stem and a scale-pan on the summit. To , , TTT . , 1 i ♦ \> 1 1 1 Nicholson's hydrometer. the lower extremity or the liydrometer two conical cups are attached; their apexes are joined so as to resemble an hour-glass; the lo^vest cone has several apertures at the top, to permit Fig. 48. 5)