V. HYDROMETERS. 1 7 1 



The same in principle and construction as the one for export, only having 

 nine extra or intermediate weights, called per cent, weights. This class of 

 instrument was only used for determining the strength of spirits imported, 

 and was adjusted slightly in favour of the importer. 



659. Set of Six Twaddell's Hydrometers. Used for 

 ascertaining the density of a solution ; principally used in trades 

 for which no special instrument of the kind is constructed. 



Dring and Fage. 



The divisions on these instruments are so placed as to indicate equal dif- 

 ferences of specific gravity. The specific gravity of a fluid is found from the 

 indication of this scale by multiplying by 5, cutting off 3 decimal places, 

 and prefixing unity. 



659a. Hydrometer by Fordyce. Royal Society. 



659b. Hicks's Patent Hydrometers, Urinometers, 

 Salinometers, &c. Hicks. 



These instruments have the scales and figures divided in black on a white 

 enamel stem, thus avoiding all errors from shifting of scale, as with paper ; 

 alteration of form, as with vulcanite ; or corrosion, as with metal. 



65 la. Tan Tester, for ascertaining the exact quantity of 

 tannic acid in any substance by passing it through a piece of hide. 



Thomas Christy and Co. 



The solution having been gauged by a tannometer before being tested and 

 after it has passed through the hide, the difference gives the exact value of any 

 tannic matter, and a merchant knowing the price of oak bark can calculate 

 the value at once of the substance he has tested. 



655. Specific Gravity Instruments, for testing liquids 

 from 650 to 900 sp. gr. L. Oertling. 



659a. Fahrenheit's Metal Hydrometer. 



The Physical Science Laboratory of the Technological 

 Institute, St. Petersburg. 



The theory of this instrument has been described and illustrated by an 

 example by E. Lenz, Academician, in the " Bulletin physico-mathematique 

 de 1'Academie des Sciences," Vol. XV., 1857. 



660. Thermo-Dilatometer, by Baudin, showing by dilata- 

 tion the per-centage strength of alcohol, from distilled water to 

 absolute alcohol 100. M. Baudin, Paris. 



661. Thermo-Dilatometer, by Baudin, showing by dilata- 

 tion the alcoholic strength of wines and other liquids, from 10 to 

 20 per cent. 



(The last two instruments are the property of the " Conservatoire 

 des Arts et Metiers.") M. Baudin, Paris. 



662. Dring and Fage Saccharometer, for ascertaining 

 the density of brewers' worts. Dring and Fage. 



