HYDRODYNAMICS. 



4.39 



upon the 



ob.-trv i 



PLATE 



lijrdrom<. specific gravity of worts. In its general appearance, 

 it is nearly the same as Jones' hydrometer, shewn in 

 ^V""' pig, 3. The stem has four sides, one of which indi- 

 cates the strength of any spirit, from alcohol to water, 

 while the other three shew the specific gravities of 

 worts. The stem has a conical form, in order to 

 make the degrees upon it more equal than they would 

 otherwise have been. A sliding rule, differing very 

 little from that of Mr Dicas, exhibits the variations of 

 density arising from changes of temperature. In using 

 this instrument, place any of the weights, if necessary, 

 i the top of the part of the stem below the ball ; 

 t- the temperature of the spirit with a thermo- 

 and bring the star of the sliding rule to the 

 degree of heat on the thermometric scale ; then the 

 strength of the spirit will be found opposite to the 

 number of the weight and the letter on the stem. See 

 a full account of this hydrometer in the Trantacliont of 

 the Society of Aril, vol. viii. p. 98. 



8. Xicholion't Hydrometer. 



The hydrometer invented by the late Mr Nicholson, 

 is superior to the ordinary instruments, both ID its ge. 

 neral construction, and from its being capable of as- 

 certaining the specific gravities of solids. This instru- 

 ment, which is shewn in Fig. 4. of Plate CCCXI V. con- 

 sists of a hollow copper ball CD attached to the dih 

 AB by means of a stem AC, made of hardened steel, 

 and about j^th of an inch in diameter. An iron stir, 

 rup E, fixed to the lower extremity of the ball, carries 

 another dish F, sufficiently heavy to keep the instru- 

 ment in a vertical position. The parts of the instru- 

 ment are so adjusted, that when 1000 grains are placed 

 in the upper dish AB, the whole will sink in distilled 

 water at the temperature of 60 of Fahrenheit, to the 

 point M in th middle of the stem. 



In order to find the specific gravity of a fluid, im- 

 merse the instrument in it, and place weights in the 

 dish AB till it sinks to the point m; then, since the 

 quantity of fluid displaced is always the same, we shall 

 have W + 1000: W=tw = S:; W being the weight 

 of the instrument, m the weight necessary to make it 

 sink to m, S the specific gravity of water, and t that of 

 the fluid. 



To determine the specific gravities of solids that do 

 not exceed 100 grains in weight, place the instrument 

 in distilled water, and, having put the solid in the dish 

 AB, throw weights into the same dish till the instru- 

 ment sinks to m. The sum of the weights added being 

 subtracted from 1000 grains, will obviously be the 

 weight of the solid, which we may call XV. Let the 

 wUd be now placed in the lower dish F, and weights 

 added in the upper dish AB till the instrument "g"*" 

 ink* to m. The weights now added, which we may 

 call ir, will be the loss of weight which the solid sus- 

 tains, or the weight of an equal bulk of distilled water, 

 consequently t : fc = W : m. As the cylindrical stem of 

 this instrument is only /,th of an inch in diameter, 

 the instrument will rise or fall nearly one inch by the 

 subtraction or addition of T ',th of a grain. It will 

 therefore indicate changes in weight less than ,%th 

 of a grain, or ^ ! - ,th of the whole ; which will give 

 gravities correct to five places of figures. 

 See Mimcheaer Memoirt, vol. ii. p. 570; and Nichol- 

 son's \atitral Pktiotophy, voL ii. p. 16. 



9. 



Hydrometer. 



I" 1 "'" instrument, which is of braw, consists of in el- 

 liptical bulb and stem, with a small loaded bulb be- 



low, for keeping it in a vertical position. The total Hydrouu- 

 length is 8 inches, the elliptical bulb is 1 J inches in x _^ e "'_ J 

 diameter and 2 inches long, and the square stem is -Jlh """Y~ 

 of an inch wide. One of the faces of the scale is used 

 for liquors that are specifically lighter than water. On 

 this face are engraven the 26 letters of the alphabet, 

 with an or zero at the beginning and end of the let- 

 ters, thus 0, A, B, C, D, &c. Z, 0. Opposite to each 

 letter, and between each of them, is a division for 

 marking the point of the stem to which the instrument 

 sinks, so that the total number of divisions is 55. The 

 weight of the hydrometer is 400 grains, and it is fur- 

 nished with four weights, viz. No. 1, 2, S, 4, which 

 weigh respectively 20, 4O, 61, and 84 grains, which 

 are placed on the instrument, below the elliptical bulb, 

 as occasion requires. These weights are adjusted in 

 such a manner, that when with one of them, such as 

 No. 9, the instrument emerges to the lower division 0, 

 it will, upon changing the weight for the next heavier 

 one, No. S, sink exactly to the other division 0, at the 

 top of the item. Hence the stem is virtually extend- 

 ed to five times its real length, and the number of di- 

 visions increased to 272 ; thus, without any weight at 

 all, it will sink exactly to the upper division in a li- 

 quor whose specific gravity is .806, and to the lower 

 division in a liquor whose specific gravity is .843, the 

 intermediate specific gravities being indicated by inter- 

 mediate divisions on the scale. By applying the weight 

 No. 1, we obtain all the specific gravities from .843 to 

 .WO; No. 2. gives them from .880 to .918 ; No. S. from 

 .918 to .58 ; and No. 4. from .950 to 1.000. When thr 

 last weight is used in water, the instrument sinks to 

 the lower at SS degrees of Fahrenheit. Each of 

 the division* on the stem will be found to correspond 

 to considerably less than an unit in the third place ot' 

 the specific gravity, and to indicate a difference of 

 about one-half per cent, or two quarts in a hundred 

 gallons. The correction for temperature is obtained 

 from a sliding rule, by an ingenious application of two- 

 scales of equal parts to each other; and the diminution 

 of bulk, or penetration as it is called, is obtained by 

 the same rule. The specific gravities, corresponding to 

 the divisions on the Mem, are likewise pointed out by 

 the sliding rule. 



Mr Atkins afterwards made considerable change* 

 upon this instrument. Instead of making the weights 

 circular, he made them of different figure*, vii. round, 

 square, triangular, and pentagonal, so as to prevent 

 any mistake being committed; and he stamps upon 

 the sliding rule, tie figure ot' the weight opposite to 

 every letter in the series to which it belongs. He has 

 also made the form ot' the great bulb cylindrical, and 

 rounded off at the upper and lower tides ; and instead: 

 of the alphabetical scale, he has engraven the real spe- 

 cific gravities on the stem of the instrument A lull 

 account of this instrument will be found in Mr Atkins* 

 pamphlet on the Ktlalion between the Specific Ciraviliet 

 and the Sirtnglfi of tijnrilu<nu Ijqttort, Lond. 1 805 ; 

 and in Nicholson's Journal, 8vo, vol. ii. p. 276, and 

 vol. iii. p. 90. 



10. Guy ton t GravaMtler. 



This instrument, which was invented by the late ce- CuvtonV 

 lebrated chemist M. Giiyton Morveau, is made of glass, gnvimct*r. 

 and carries two basins like the hydrometer of Nichol- 

 son. The bulb is cylindrical, and is connected with the 

 upper basin by a slender stem, in the middle of which 

 is the fixed point of immersion. The lower basin, 

 which terminates in a point, contains the ballast, and i* 



