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TABLES FOR REDUCING THE DEGREES OF BEAUME’s AREOMETERINTO THEIR CORRESPONDING EXPRESSION OFSPECIFIC GRAVITY.
Beaume’s Areometer or Hydrometer, though not a very correct inftrument, is that which fromits convenience is employed very commonly by the French chemifts, who are in the habit ofexpreffing the ftrength or fpecific gravity of the acids, alcohol, &c. which they employ by thefcale of this inftrument. It is deferibed by Beaume in his Elemens de Pharmacie, p. 406.
The form of this inftrument is that of the common hydrometer, that is, a lengthened'bulbor ball with a long narrow Item rifing from it, which laft is graduated, and the inftrument is Iopoifed that it floats with nearly the whole of the ftem above the level of the heavieft liquid wholedenfity it is to indicate, and with nearly the whole of the ftem immerfed when the lighteft liquidis ufed. A Angle inftrument would in ftriftnefs fufftce to indicate the denfitv of every liquid fromthe lighteft alcohol to the heavieft acid, which would include a range of adfual fpecific gravity fromabout .8 to 2. (water being — 1.) But an inftrument of this kind mull be either inconveni-ently long, or the ftem muft be very wide, and the degrees too minute for tolerable accuracy.Beaume therefore very judicioufly divided it into two feales, one of which is the areometer forfpirits and liquors lighter than water, and the other the areometer for falts or liquids heavier thanwater. He has further diftinguifhed them by inverting the feales, that is to fay, in the inftru-ment for falts the o. or zero is at diftilled water, and the numbers increafe with the increaftngdenfity of the liquors for which it is ufed ; whereas in .the inftrument for fpirits the numbersincreafe from the zero with the decrcafing denfity. Hence it is neceffary to deferibe thefe twoinftruments feparately.
The hydrometer for falts was made by Beaume in the following way: the inftrument wasfirft immerfed in'water at 18.75° Reaum. m about5©°. Fahr. and loaded with mercury droppedinto the bulb till it funk fo low that only the very top of the ftem was but of water, which pointwas marked as the o. of the fcale. The inftrument was then removed to a folution of commonfait, containing 15 parts (by weight) of fait to 85 parts of water, and the height to which itfloated was marked on the ftem as 15° of the fcale. The interval between thefe two points ofimmerfion being therefore confidered as 15 degrees, the fcale was extended to any requirednumber, merely by marking off with compaffes an equal length of the~ftem, and the whole wasfarther fubdivided in the fame way. Beaume confidered therefore that every degree of theinftrument indicated a denfity of liquid equal to that of a folution of common frit, in which thenumber of parts of fait in ioo parts, by weight, of the folution, was equal to the fame numberon the fcale at which the inftrument floated. But as the diameter of the ftem is feldom equalthroughout, he propofes to remedy the incorredhiefs produced by this circumftance, wheregreater accuracy is required, by immerfing the inftrument fucceflively in folutions containing 5,10, 15, &c. per cent, of fait, and marking thefe points as 5, 10, ijj &c. on the fcale, or, to beftill more accurate, all the individual degrees may be found by aflual experiment. In faff, evenwhere the ftem of the inftrument is perfedtly cylindrical, this would be the only way to enfureperfedb accuracy, as a divifion of equal diftances on the fcale would not precilely correfpondwith an equal increafe of the percentage of fait in the folution.
The fcale of this inftrument does not properly extend higher than about 30°. as this is thepoint of faturation of water with fait, but it may be lengthened at pleafure by marking oft equaldiftances on the fcale.
The following table of correfpondence between Beaume’s areometer for falts and the actualexpreffion of fpecific gravity has been calculated by Mr. Nicholfon, for every third degree(Phil. Journ. 4to. vol. i. p. 38.) from the datum of Morveau that the 66th degree correfpondswith 1.848 fp. gr. We have added to it the fpecific gravities of rnoft of the correfponding folu-tions of common fait in water as high as 30°. of the inftrument, as given by Haffenfratz in the28th vol. of the An. de Chim. p. 298. which ought therefore to be the fame, but which actuallydiffer in no inconfiderable degree.
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