Hydro meters. temperature of the standard of length. Under these conditions the coefficient of conversion for barometrical measurements is the same as for linear." and As the metre has its true or legal length at 0° C., the yard has its true or legal length at 62° F., we can only find the true or legal difference between the two measures when we take the one at 0° C., and the other at 62° F. For the purpose of determining the degree of gravity of spirits the only hydrometer known to the law is that of Sikes," and Mr. R. Bannister, the Deputy Principal of the Government Laboratory at Somerset House has kindly furnished the writer with the following information with reference to Sikes' hydrometer. The hydrometer at present used for levying the duty cn spirits is that of Sikes, which was legalised by Act 58 Geo. 3 c. 28 (1817). It is made of brass, gilt, the spherical bulb being fitted with a stem at either pole. The upper stem bears the scale of 10 main divisions, each of which is again divided into five parts, giving 50 sub-divisions in all. The lower stem serves to secure upright flotation and to carry the weights by means of which the range is extended to 500 sub-divisions representing about 185 degrees of gravity. Sikes' instrument does not, however, indicate specific gravity (sp. gr.), but shows by the help of tables (Tables for ascertaining the Strength of Spirits with Sikes' Hydrometer) the "strength " over or under "proof” of the sample examined. A definition of "proof" is given in terms of sp. gr. in the Act as that which at 51° F. weighs exactly twelve-thirteenths of an equal bulk of distilled water. The technical terms "over" and "under proof will be readily understood from the following: Spirit is a overproof (o. p.) when 100 gallons of it will produce (100+) gallons at proof by dilution with underproof (u. p.) when 100 gallons of it x) gallons of proof spirit. For raising the duty on beer a direct sp. gr. instrument, or gravimeter with poise weights, termed Bate's Saccharometer, is in use. It is a gilt brass instrument, constructed on the same principle as the hydrometer, and shows specific gravities at 60° Fahrenheit. By means of an admirable contrivance in the size and weight of the poises the same stem is used for 180 degrees of specific gravity. This instrument and tables for temperature corrections have been in use since 1829. Turning now to the means adopted for verification, the Saccharometer, showing as it does the sp. gr. of the solution in which it floats, is controlled directly by the gravity bottle; the hydrometer is compared with the standard instrument, which in turn is controlled by comparison of its weight and volume with data derived from Sikes' original instrument. The alcoholmeter used by Her Majesty's Customs is also Sikes' hydrometer, as the Customs laws impose a duty on spirits according to the proof gallon, and it is necessary to use an instrument formed so as to show the gravity of any mixture of alcohol and water in which it is immersed. The brass bulb of a hydrometer, being thin and hollow, renders the instrument liable to injury from abrasion or rough treatment, and from the incrustation of the colouring matters of the liquids tested. From any of these causes it is easily put out of order, so that its accuracy requires to be carefully tested from time to time by comparison with standard instruments. When a Sikes' hydrometer is inaccurate to the extent of a quarter of one degree marked on the stem, it is considered to be out of order. The United States Government adopted standard hydrometers made of glass and not of metal, but glass instruments are of course more easily broken, although the ordinary hydrometers and saccharometers, &c., used by chemists are mostly made of glass. Other hydrometers are also used in determining the specific gravities of various liquids; for instance, Beaume's hydrometers (1) for fluids heavier than water, (2) for fluids lighter than water, and M. Francœur has given the following table of specific gravities corresponding with Beaume's hydrometer at 541° F. The centesimal alcoholmeter of Gay Lussac is also used ("Instruction pour l'usage de l'Alcoomètre Centésimale." Par M. Gay Lussac. Paris, 1824). To determine the quantity of water contained in ardent spirits, Gay Lussac took pure alcohol by volume at 15° C. and represented its strength by 100 per cent., or unity; hence the strength of a liquor is simply the per cent. by volume of pure alcohol which it contains at 15° C., at which temperature this hydrometer is graduated from 100 (alcohol) to () (water), each graduation or degree of the scale representing a per cent. of alcohol. Tralles' centesimal alcoholmeter differs very slightly from Gay Lussac's. The specific gravity of water is taken by Tralles as unity at its maximum density (4° C.), so that it becomes 0.9994 at 60° F.; whereas Gay Lussac assumed the unity of water at 15° C.; and took the specific gravity of absolute alcohol at 0.7947 (t = 15° C.) while Tralles took 0.7939 (t = 60° F.), Tralles based his result (1811) on the weighings of water by Gilpin and Blagden (Phil. Trans. Roy. Soc. 1790) and Gay Lussac on his own experiments in 1824. Both weighings of water have, however, been now superseded (see p. 88) by more accurate weighings (see also " Mémoire sur l'aréometrie." Francœur, Paris, 1842. "United States Reports on Sugar and Hydrometers" made by Prof. A. D. R. S. McCulloh. Washington, 1848. of Arts and Manufactures," 1843, p. 23. Bache and Prof. Ure's " Art. "alcohol"). Standards. Indirectly derived from scientific measuring instru- Gasments are the standards used in the sale of gas, regulated measuring by the Sale of Gas Act, 22 & 23 Vict. c. 66, 1859; 23 & 24 Vict. c. 146, 1860; and the Gas Works Clauses Act (1847) Amendment, 1871. The Act of 1859 provides that the only legal standard or unit of measure for the sale of gas by meter shall be the cubic foot containing 62.321 lbs. avoirdupois weight of distilled or rain water weighed in air at the temperature of 62° F. thermometer, the barometer being at 30 inches. The actual Board of Trade standards for the measurement of gas are known as "gasholders," and in 1861 under the direction of H.M.'s Treasury three such standard gasholders of the cubic foot, 5 cubic feet and 10 cubic feet, were deposited with the Comptroller-General of the Exchequer, and were subsequently transferred to the Board of Trade in 1866. Copies of these models were also sent in 1862 to the Lord Mayor of London, and to the chief magistrates of Edinburgh and Dublin respectively; and other copies have since been obtained by the local authorities of other cities and boroughs. A standard of 20-cubic feet was also added in 1893. By means of such copies the local inspectors of gas meters, who are appointed by the local authorities, test the gas meters fixed on consumers' premises. No practical alteration has taken place in the mode of measuring gas since these standards were made in 1861; excepting in some improvements in detail, the same forms of "wet" meter and "dry" meter being still used in the sale of gas. On every consumer's meter tested and stamped by an inspector a stamp of the following official design should appear. Besides the official stamp of verification the stamp of the local authority is placed by the inspector on the meter. The Sale of Gas Act, 1859, allows an inspector to pass any meter which is not more than 3 per cent. in favour of the consumer and 2 per cent. in favour of the seller of gas, so that two stamped meters might vary 5 per cent. The standard cubic foot itself is actually determined by means of a conical copper vessel or "bottle" holding a cubic foot of water, and not by means of any vessel of rectangular shape; the probable error of measurement being less in the use of a measure of conical shape holding a cubic foot of water than in a cubed measure of the dimensions of 1 foot. |