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164
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HYDROMETER


from 29 under proof to pure water, the graduation corresponding to which is marked W at the bottom of the fourth scale. One side of the stem AD is shown in fig. 5, the other three in fig. 6. The thermometer is also provided with four scales corresponding to the scales above mentioned. Each scale has its zero in the middle corresponding to 60° F. If the mercury in the thermo-9 @ meter stand above this zero the spirit must be reckoned weaker than the hydrometer in-H - dicates by the number on the thermometer lg: scale level with the top of the mercury, while E', E EI if the thermometer indicate a temperature 5 E I lower than the zero of the scale (60° F.) the E E spirit must be reckoned stronger by the scale § E: reading. At the side of each of the four E scales on the stem of the hydrometer is en-El graved a set of small numbers indicating the contraction in volume which would be experi§ EQ enced if the requisite amount of water (or Tj spirit) were added to bring the sample tested § to the proof strength.

§ The hydrometer constructed by Dicas of Liverpool is provided with a sliding scale which

FIG. 6.

can be adjusted for different temperatures, and which also indicates the contraction in volume incident on bringing the spirit to proof strength. It is provided with thirty-six different weights which, with the ten divisions on the stem, form a scale from 0 to 370. The employment of so many weights renders the instrument ill-adapted for practical work where speed is an object.

This instrument was adopted by the United States in 1790, but was subsequently discarded by the Internal Revenue Service for another type. In this latter form the observations have to be made at the standard temperature of 60° F., at which the graduation 100 corresponds to proof spirit and 200 to absolute alcohol. The need of adjustable weights is avoided by employing a set of five instruments, graduated respectively°-100°, 80 -120°, 100°-140°, 130°-170 °, 160°-200°. The reading gives the volume of proof spirit equivalent to the volume of liquor; 2 thus the readings 80° and 120° mean that 100 Volumes

0 amount

volumes

spirit is

of the test liquors contain the same of absolute alcohol as 80 and 120

of proof spirit respectively. Proof

defined in the United States as a

mixture of alcohol and water which contains equal volumes of alcohol and water at 60° F., the alcohol having a specific gravity of 0-7939 at 60° as compared with water at its maximum density. The specific gravity of proof 'spirit is 0-93353 at 60°; and 100 volumes of the mixture is made from 50 volumes of absolute alcohol and 53-71 volumes of water.

Quin's universal hydrometer is described in the Transactions of the Society of Arts, viii. 98. It is provided with a sliding rule to adapt it to different temperatures, and has four scales, one of which is graduated for spirits and the a other three serve to show the strengths of worts. The peculiarity of the instrument consists in the pyramidal form given to the stem, which renders the scale-divisions more nearly equal in length than they would be on a prismatic stem.

Atkins's hydrometer, as originally constructed, is described in Nicholsonlv Journal, 8v0, ii. 276. It is made of brass, and is provided with a spheroidal bulb the axis of which is 2 in. in length, the conjugate diameter being 1% in. The whole length of the instrument is 8 in., the stem square of about 5-in. side, and the weight about 400 grains. It is provided with four weights, marked 1, 2, 3, 4, and weighing respectively 20, 40, 61 and 84 grains, which can be attached to the shank of the instrument at C (fig. 7) and retained there by the fixed weight B. The scale engraved upon one face of the stem contains fifty-five divisions, the top and bottom being marked 0 or zero and the alternate intermediate divisions (of which there are

wenty-six) being marked with the letters of the alphabet in order.

The four weights are so adjusted that, if the instrument lioats with the stem emerging as far as the lower division 0 with one of the weights attached. then replacing the weight by the next heavier causes the instrument to sink through the whole lens;/the of the scale to the upper division 0, and the first weight produces the same effect when applied to the naked instrument. The stem is thus virtually extended to five times its length, and the number of divisions increased practically to 272. When no weight is attached the instrument indicates densities from ~806 to -843; with No. 1 it registers from -843 to -880, with No. 2 from -880 to -918, with No. 3 from -918 to ~958, and with No. 4 from -958 to 1-000, the temperature being I

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74

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C

F v. V

B

FIG. 7.-Atkins's

Hydrometer.

55° F. It will thus be seen that the whole length of the stem corresponds to a difference of density of about -04, and one division to about 'OOO'}'4, indicating a difference of little more than § % in the strength of any sample of spirits.

The instrument is provided with a sliding rule, with scales corresponding to the several weights, which indicate the specific gravity corresponding to the several divisions of the hydrometer scale compared with water at 55° F. The slider upon the rule serves to adjust the scale for different temperatures, and then indicates the strength of the spirit in percentages over or under proof. The slider is also provided with scales, marked respectively Dicas and Clarke, which serve to show the readings which would have been obtained had the instruments of those makers been employed. The line on the scale marked “ concentration ” indicates the diminution in volume consequent upon reducing the sample to proof strength (if it is over proof, O.P.) or upon reducing proof spirit to the strength of the sample (if it is under proof, U.P.). By applying the several weights in succession in addition to No. 4 the instrument can be employed for liquids heavier than water; and graduations on the other three sides of the stem, together, with an additional slide rule, adapt the instrument for the determination of the strength of worts. Atkins subsequently modified the instrument (Nicholsorfs Journal, 8vo, iii. 50) by constructing the different weights of different shapes, viz. circular, square, triangular and pentagonal, instead of numbering them 1, 2, 3 and 4 respectively, a figure of the weight being stamped on the sliding rule opposite to every letter in the series to which it belongs, thus diminishing the probability of mistakes. He also replaced the letters on the stem by the corresponding specific gravities referred to water as unity. Further information concerning these instruments and the state of hydrometry in 1803 will be found in Atkins's pamphlet On the Relation between the Specific Graz/ities and the Strength of Spiriluous Liquors (1803): or Phil. Mag. xvi. 26-33, 205-212, 305-312; xvii. 204-210 and 329-341.

In Gay-Lussac's alcoholometer the scale is divided into 100 parts corresponding to the presence of x, 2, . . % by volume of alcohol at II5° C., the highest division of the scale corresponding to the purest a cohol he could obtain (density -7947) and the lowest division corresponding to pure water. A table provides the necessary corrections for other temperatures.

Tralles's hydrometer differs from Gay-Lussac's only in being graduated at 4° C. instead of 15° C., and taking alcohol of density 7939 at 15~5° C. for pure alcohol instead of -7947 a s taken by Gay, Lussac (Keene's Handbook of Hydrornelry). In Beck's hydrometer the zero of the scale corresponds to density I'0OO and the division 30 to density -850, and equal divisions on the scale are continued as far as is required in both directions. In the centesimal hydrometer of Francoeur the volume of the stem between successive divisions of the scale is alwaysiggth of the whole volume immersed when the instrument floatsin water at 4° C. In order to graduate the stem If the instrument is first weighed, then immersed in I distilled water at 4° C., and the line of flotation E [Fil F marked zero. The first degree is then found by placing on the top of the stem a weight equal to E fimth of the weight of the instrument, which in- E creases the volume immersed by 12,0th of the original volume. The addition to the top of the stem of D E successive weights, each limth of the weight of the E instrument itself, serves to determine the succes- f sive degrees. The len th of 100 divisions of the Q scale, or the length of the uniform stem the volume E of which would be equal to that of the hydrometer E up to the zero graduation, Francoeur called the “modulus " of the hydrometer. He constructed, fr-e his instruments of glass, using different instruments ' for different portions of the scale (Francceur, T raité dnréométrie, Paris, 1842). “=§ f~” lf Dr Boriés of Montpellier constructed a hydro- " meter which was based upon the results of his C experiments on mixtures of alcohol and water. The interval between the points corresponding to B ' E pure alcohol and to pure water Boriés divided into 100 equal parts, though the stem was pro- F IG. 8.-Sikes's longed so as to contain only IO of these divisions, Hydrometer. the other 90 being provided for by the addition of 9 weights to the bottom of the instrument as in Clarke's hydrometer. The instrument which has now been exclusively used for revenue purposes for nearly a century is that associated with the name of Bartholomew Sikes, who was correspondent to the Board of Excise fxiiom 1774 to 1783, and for some time collector of excise for Hertfords ire.

Sikes's hydrometer, on account of its similarity to that of Boriés, appears to have been borrowed from that instrument. It is made of gilded brassor silverfand consists of a spherical ball A (fig. 8), 1-5 in. in diameter, below which is a weight B connected with the ball by a short conical stem C. The stem D is rectangular in section and about 3% in. in length. This is divided into ten equal parts, each of which is subdivided into five. As in Boriés's instrument, a series

of 9 weights, each of the form shown at E, serves to extend the scale