440 



HYDRODYNAMICS. 



-Hydrome attached to the cylinder by two branches. The cylinder 



ters. j s 6.85 inches long, and 0.71 in diameter. The upper 



"~v~""' basin carries an additional constant weight of 1 1 5 grains. 



Guyton's To this apparatus, M. Gnyton has added another piece, 



graviuieter. which he calls the Plongeur, or plunger, which is a ball 



of glass loaded with mercury, till its total weight may 



be equal to the additional weight of 115 grains, added 



to the weight of the volume of water displaced by the 



plunger. The plunger is always placed in the lower 



basin when it is used ; and it will readily be seen, that 



the gravimeter will sink to the same mark on the stem 



whether it is loaded with the constant weight of 115 



grains in the upper basin, or with the plunger in the 



lower basin. 



. The object of this instrument is to ascertain, 1st, 

 The specific gravities of solids, whose absolute weight 

 is less than 115 grains ; 2d, Of liquids inferior to wa- 

 ter in specific gravity ; 3d, Of liquids of greater speci- 

 fic gravity than water ; 4th, The absolute weight of bo- 

 dies below 1 15 grains ; and, 5th, The degree of rare- 

 faction and condensation of water in proportion to its 

 bulk, the purity of the water being previously known. 

 In order to find the specific gravity of any solid by 

 this instrument, place the solid in the upper basin, and 

 add weights till the instrument sink to the fixed point 

 of immersion. Subtract these weights from the con- 

 stant weight of 1 1 5 grains, and the remainder is the 

 absolute weight of the solid. Multiply this by the spe- 

 cific gravity of the fluid, and reserve the product, place 

 the solid in the lower basin, and add weights in the up- 

 per basin till the instrument sinks to a fixed point of 

 immersion ; and subtracting these additional weights 

 from the additional weights when the body was in the 

 upper basin, the remainder will be the loss of weight 

 by immersion. Divide the reserved product by this loss 

 of weight, and the quotient will be the specific gravity 

 of the solid with regard to distilled water at the stan- 

 dard temperature and pressure. 



In order to find the specific gravity of a fluid, immerse 

 the gravimeter in the fluid, and having observed the 

 weight which is necessary to sink it to the fixed point of 

 immersion, add this weight to that of the gravimeter. 

 To the weight required to sink it in distilled water, add 

 also the weight of the gravimeter. Divide the first sum 

 by the second, and the quotient will be the specific gra- 

 vity of the fluid. See the Annales de Cliimie, vol. xxi. 

 p. 3 ; and Nicholson's Journal, 4to, vol. i. p. 110. 



1 1 . Specr's Hydrometer. 



Speer's hy- This instrument consists of a ball and stem, with a 

 counterpoise underneath. The stem is cut into an oc- 

 tagonal form ; and upon each of the eight faces of the 

 octagon is engraved a scale of per centages, by the in- 

 spection of which the strength of the spirit may be 

 found. The scale upon each of the faces is suited to 

 the temperatures of 35, 40, 45", 50, 55, 60, 65, and 

 70". When the temperature of the spirits is found by 

 the thermometer, their strength must be sought on that 

 face of the octagon which corresponds with the temper- 

 ature. As the temperature is indicated only to every 

 five degrees, there is an index which performs the of- 

 fice of a weight, for pointing out the effect for inter- 

 mediate temperatures. The precision of a single de- 

 gree of the thermometer may also be obtained by four 

 small pins, which are inserted in holes in the counter- 

 poise below, where they operate as weights of adjust- 

 ment, and produce the same effect as a variation of tem- 

 perature. For a full account of this hydrometer, see 



Speer's Enquiry into the Causes ef'thc Errors and Irre- Hydrome. 

 gnlarities which take place in ascertaining the Strength ^ " 

 of Spirituous Liquors by the Hydrometer. Lond. 1802; ^""Y"^"*' 

 Philosophical Magazine, vol. xiv. p. 151 ; and the Ee- 

 perlory of Arts, 2d series, vol. iii. p. 81. 



12. Mr Adie's Statical Hydrometer. 



This hydrometer, which is one of the neatest and most Adie's sta- 

 correct instruments that we have seen, was first con- tical hydro- 

 structed about the year 1799 by Mr Adie, optical in- p eter - 

 strument maker in Edinburgh. It is made entirely of cccJUV 

 brass, and consists of a lever AB 10^ inches long, resting pig. 5. 

 upon a fulcrum C, so that the shorter arm AC is 2^ 

 inches, and the longer one CB 8 inches long. At the 

 extremity A of the shorter arm is suspended a brass 

 ball, whose solid content is -r-J^. of a gallon. This ball 

 is immersed in the fluid which is held in the cylindri- 

 cal brass jar FG. Two moveable weights m, n, slide 

 along each arm of the balance. When the temperature 

 of the spirits is found by the thermometer, the weight 

 m is set to the corresponding degree upon the thermo- 

 metric scale AC. The weight n is then moved along the 

 other arm CB, till the ball E is in equilibrium in the 

 fluid, which is indicated by the coincidence of the arm 

 CB with the horizontal index o, fixed to the bar b. The 

 whole of this instrument is nicely packed into a maho- 

 gany box 1 1 inches long and 2^ square, which serves 

 as a stand for the balance. 



13. Mr Adie's Sliding Hydrometer. 



The sliding hydrometer, invented by Mr Adie, dif- Adie's sli- 

 fers from all other hydrometers, in requiring no weights ding hydro* 

 whatever for its adjustment. It is a floating hydrome- meter. 

 ter, of the usual form ; but instead of being adjusted 

 by weights, the volume of the instrument is increased 

 by drawing out a tube, while its weight is invariable. 

 If the instrument sinks to the fixed point of immersion 

 in distilled water, before the tube is drawn out, it is 

 obvious that in spirituous liquors, it may be made to 

 sink to the same point, merely by drawing out a tube 

 below the principal bulb ; for the same effect is thus 

 produced by increasing the volume of the instrument, 

 as if its weight were diminished. 



14. Charles's Thermomelrical Hydrometer. 



This instrument, which, we believe, has been descri- Charles's 

 bed for the first time by M. Biot in his Traite de Phy- tliermome- 

 sique, torn. i. p. 414, was invented by M. Charles, to trical hydro* 

 whom experimental philosophy is under great obliga- meeer - 

 tions. It is called a thermometrical hydrometer, from 

 its being employed to measure the densities of water at 

 different temperatures. In order to give a very high 

 degree of sensibility to the instrument, M. Charles 

 makes the ball very large, and the stem very small ; 

 the augmentation of the ball rendering the absolute ef- 

 fects of the dilatation more considerable, and the small- 

 ness of the stem enabling us to measure these dilata- 

 tions upon a greater scale. The whole instrument, 

 with the basin for holding the weights, weighed in air 

 90.303 grammes, or 90.4209 when reduced to a vacuum. 

 An account of the results obtained with this instrument 

 will be found in M. Biot's work. 



15. Charles's Balance Areometer. 



Charles's 



This hydrometer, which is intended to measure the balance are- 

 ometer. 



