I. SPECIAL COLLECTIONS. 157 



apparent specific gravity of that liquid at the observed tempe- 

 rature will be - 



580. Instruments (Nos. 2 and 3) for ascertaining the strength 

 of alcoholic liquors. The degrees are the same as in No. 1, but the 

 weight is not variable, and the zero is the immersion point at 

 15 C. in a liquid, of which the specific gravity at that temperature 

 is equal to the specific gravity of pure water at 4 C. Tables are 

 added, those of Professor von Baumhauer (1863), used in Holland ; 

 those of the exhibitor (1873), used in the colonies. The latter are 

 based on the researches of MendekjefF. Phil. Mag. (4) XXIX. 

 395.) 



581. Hydrometer (No. 4), for liquids of a specific gravity 

 greater than 1. The construction is the same as in Nos. 2 and 3. 

 The Beaume scale is added. Used for solutions of salts and sugar 

 juices. 



582. Hydrometers (Nos. 5 and 6), for ascertaining the 

 specific gravity of seed oils and of petroleum, allowing immediate 

 application of correction for temperatures above or below 15 C. 

 (For description see Scheik. Bijdragen door J. W. Gunning, 

 Amsterdam, 1867.31.) 



583. Densimeters (Nos. 7, 8, and 9), with flat stems. The 

 zero is the same as in Nos. 2 and 3. 



584. Hydrometer (No. 10), for preparing a liquid having at 

 15 C. the specific gravity of pure water at 4 C. The instrument 

 is made in the following manner : Through the open stem shots 

 are introduced till the instrument floats at the mark on the stem in 

 pure water of 15 C. The weight of the instrument is then 

 increased in the ratio 0-99915 : 1, in consequence of which it floats 

 at the same mark at 15 C. in a liquid having at that temperature 

 the specific gravity of pure water at 4 C. 



585. Trough for comparing Hydrometers. 



Thermometers. The instruments have the Celsius' scale. 

 By their mode of construction they possess the following advan- 

 tages : (1.) They may be turned upside down and shaken in any 

 manner without breaking the column of mercury. (2.) Though 

 newly made, the zero is not subject to displacement. 



The former advantage is obtained by filling the tube and the 

 upper space with perfectly dry air, free from dust, as highly com- 

 pressed as possible. 



The latter advantage is secured by placing the bulbs of the 

 newly made' thermometers in a bath of paraffin, heated slowly to 

 100 C. and then 'allowed to cool slowly and in succession sixty to 

 a hundred times. 



